Is it usual?

Less than the maximum 90 days in 180 is quite usual, though I suspect the full 90 days is more common. 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.

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.