score:3
Is it usual?
Less than the maximum 90 days in 180 is quite usual (per @Henning's Comment below - the norm for single-entry visas), though I suspect the full 90 days is more common (if considering both single and multiple entry visas). What is a little unusual is no margin - a few days is often rounded to a week or 11 days rounded to 15.
Does it work this way?
Clearly it does. You got what you asked for. Had you asked for more you might have been allowed more but the chances of being granted a visa may have been a little less.
Upvote:2
Yes it absolutely works this way; especially if this is your first time applying.
My very first Schengen visa was granted exactly for the duration of the stay as well.
The 90 days you mention is the maximum allowed (per 180 day period); but it is subject to your visa being granted for that length of time.
Unlike the US and some other countries, a Schengen visa must be valid throughout the duration of the visit.
Your visa is valid for exactly the dates and days mentioned on it.