But there is a plugin for this case...

The argument against this idea is that a large majority of the WordPress userbase does not need to know this information.

This isn't IMHO really an argument - WP has a few other features (e.g. posting via mail) that are useful only for a minority... Not speaking about that simple solution to hide IDs defaultly and make it possible to turn them on in Screen options (or ev. in global settings).

I agree this was one of the not-so-much-thoughtful touches on 2.5.