Is meditation necessary in Buddhism?

Meditation is necessary for the purification of the mind and freedom from suffering. If anyone has intention for these things, there is no other way than meditation to lead him/her to the right direction. Also it is better to be clear about what "meditation" really is: https://buddhism.stackexchange.com/a/33048/700

But Buddha knew that the vast majority of the humans would never interested in meditation so he gave a teaching that in each generation few people would realize Nibbana in one life time and few others would start on the path of freedom from suffering although the real training on the dhamma starts after the realization of Nibbana.

Buddhism has all kinds of followers and it is not a Buddhist way to say that "you are not Buddhist" to the people who are not interested to meditation. The precepts and Buddhist principles makes the non-meditator Buddhists little bit better than many people in the world while things like "killing" is a natural and even admirable thing in many places of the world. But the truth is precepts/Buddhist principles and meditation(mindfulness) support eachother. If a person isn't interested in meditation it would be very difficult for him/her to follow the precepts and be a good person in general. In fact in the long term it would be impossible.

Right concentration is a factor that arises out of it's causes and not something that is pulled out or in. The path develops based on right view and right concentration is of course a part of the way to liberation. But it's of no use to pull in, put out effort right there. Therefore one with confidence focuses on right effort to straighten right view and make all conditions better to develop the path. And what is right effort as a path element?

"One tries to abandon wrong view & to enter into right view: This is one's right effort...

"One tries to abandon wrong resolve & to enter into right resolve: This is one's right effort...

"One tries to abandon wrong speech & to enter into right speech: This is one's right effort...

"One tries to abandon wrong action & to enter into right action: This is one's right effort...

"One tries to abandon wrong livelihood & to enter into right livelihood: This is one's right effort." — MN 117

To come their possible later or in other existances, one living in the house trains generosity, Sila, Dhamma-reflection (of the burdens), since even if good will mostly have a problem at right livelihood (of which the highest is nourish some happiness by dwelling in concentration, while living on alms for the bodies welbeing).

(That's not given for trade, exchange or entertainment but for liberation only)

Yes, it is if the layperson is aiming for awakening in this very life. Two of the factors of the eightfold path directly correspond to meditation - sati and samadhi.

Is the practice of Buddhism incomplete without meditation?

This might be a controversial answer, but yes. It is. Except for those who are born with immense conscious bandwidth, stable concentration and clear mindfulness meditation is an indispensable part of the spiritual path. This is the path of purification.

Over time, in certain Buddhist countries the goal of spiritual practice diverged between the laity and monastics.

The laypeople aim for a better rebirth and accumulate "merits". This is quite non-Buddhist in nature if you examine it closely as there is no one gaining merit, possessing merit or keeping track of merit. This is a modern adaptation and a very ego-self oriented one at that.

It is this divergence in certain Buddhist countries that gave rise to the belief that meditation is for monastics and the laity is there to support monastics and hope for a better rebirth.

It is an unfortunate misconception as teachers like most of the Thai Ajahns, Burmese Sayadaws, teachers of the Vipassana movement, Western teachers like Culadasa, and countless other teachers have spent their time to share the immensely valuable resources for us laypeople to practice. It is a blessing and we should not throw that away in the face of dogma.

Lastly, if you go into Mahayana , Vajrayana traditions there is no question that not only is meditation important to laypeople but laypeople can even guide other beings along the path.

All compounded things are subject to vanish. Strive with earnestness.

My teacher said, the key difference between those Buddhists that only speculate based on the theories they read in books, and those Buddhists that actually know what they are talking about, is meditation.

Meditation and the Noble Eightfold Path is necessary for Buddhist enlightenment but it is not a compulsory practise for Buddhist lay people (non-monks). The Dhammacakkappavattana Sutta) says:

There are these two extremes that are not to be indulged in by one who has gone forth [from the household life]. Which two? That which is devoted to sensual pleasure with reference to sensual objects: base, vulgar, common, ignoble, unprofitable; and that which is devoted to self-affliction: painful, ignoble, unprofitable. Avoiding both of these extremes, the middle way realized by the Tathagata — producing vision, producing knowledge — leads to calm, to direct knowledge, to self-awakening, to Nibbana. And what is the middle way realized by the Tathagata... Precisely this Noble Eightfold Path: right view, right resolve, right speech, right action, right livelihood, right effort, right mindfulness, right concentration.

For Buddhist lay people, they should ideally at least practise the five moral precepts of training in non-killing, non-stealing, non-sexual-misconduct, non-lying & non-drug-alcohol taking. Also, avoiding worse bad things, such as gambling, addictions to entertainment, indebtedness & laziness. Refer to the Sigalovada Sutta for the The Layperson's Code of Discipline.

Also, fully completing the last factor of the Noble Eightfold Path, namely, Right Samadhi, is not required for the 1st stage of enlightenment, called "stream-entry".

There is a preliminary level of right samadhi called "neighbourhood concentration". It does not reach "absorption" yet it is "right" because it has a foundation of Right Understanding or non-clinging. It is clear enough for the development of insight.