Why all dates columns in drupal are type=int and not type=date/timestamp/time? I want to make this question short, so as title says "Why all dates in drupal are INT" ?

I've notice that in Schema API there was "datetime" but it was removed in D7. 
Also all tables that have time in it (cache_*,semaphore,node etc.) have INT instead of TIMESTAMP.

Before debating "INT vs TIMESTAMP" flame, I would like to remind you that:


DATETIME is obvious what the value represents.  
INT is smaller 
TIMESTAMP has both advantages.


The thing is that I want to understand what's "philosophy of drupal" for this.
I guess the main reason its that you cannot have two columns with TIMESTAMP and default NOW() value in MySQL according the documentation (see that answer). So seems to be the easier way to workaround it its to use int.