Besides Magna Carta and general decentralization, what specifically led to democratization in England?

Even earlier than the Glorious Revolution, I recall reading the Hundred Years' War between the royal dynasties of England and France from 1337 to 1453 also played an important role in building the foundations of democracy in England.

The English kings were forced to finance the war effort (which was not universally popular) with the aid of Parliament and thus conceded authority to that early democratic institution. England's ultimate defeat in the Hundred Years' War was partially responsible for the War of the Roses which split the English nobility into opposing factions and further weakened the Crown.

In contrast, the Hundred Years' War allowed the French monarchy to increase its central authority and taxation powers for the defense of the home soil. The French kings were less dependent on national legislatures for raising money than England. In fact, Charles VII established a standing army in 1445, which England did not have for another two hundred years.

It wasn't just "weakening of central government", but more specifically, weakening of the King/Queen, giving Parliament more power. The Magna Carta was part of that.

Another notable event was the Glorious Revolution in 1688 when Parliament kicked the (Catholic) King James II out and replaced him with the Dutch. This is another example of Parliament (i.e. the nobility) limiting the powers of the King.

Over the years, Parliament got more democratic as they allowed more people to vote, cf. Reform Act

There was a medieval saying, "Stadluft macht Frei." (City air makes one free.)

One important aspect of England (and Greece and Rome before it) was the relative urbanization of its time. The most "progressive" and democratic elements of society tend to concentrate in cities, whereas the most conservative and pro monarchic influences are generally found in the countryside.

A major test of England's progress toward democracy was the English Civil War of the 1640s, which at its core, pitted the new urban elite against the agrarian nobility. (The former won.) Cities like London and York (to a lesser extent, Liverpool and Bristol) housed manufacturing interests that tended to support democracy, or at least provide protection from the feudal lords. In Poland and the Holy Roman Empire, there were fewer cities representing a smaller proportion of the population keeping the nobles in check.

In addition to the points already made, I would say that religion might have played a major role in how England turned out. The English Civil War and the Glorious Revolution, both of which severely damaged the power of the monarch (the former completely destroying it for a while) were partly because of religion.

Structures like the English Parliament were already in place to take advantage of the weakening of the power of the monarch or the nobility for that matter.

A second reason I stress the above two events is that even as late as the mid-16th century (end of the reign of Henry the VIII), the monarch had an extreme amount of power and democracy really started emerging during the mid-17th century.

In addition to what you list, the organizational structure, bookkeeping of the monarchs, and relative literacy levels (albeit not high levels absolutely) helped enable a democratic system to emerge.

• Townhalls and church organizations allowed for some census and accountability to emerge.
• The later monarchs kept relatively accurate and complete tax records which also helped a census and popular organizational structure emerge.
• As law enforcement developed and shires, counties and the like saw division of municipal resources and enforcement, popular organization flourished as well.