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.