It does show the timestamp, just in the main header instead.

For example, in http://bs.wikipedia.org/?diff=130 (one of the examples you gave) there is a header:
Verzija 00:40, 13 decembar 2002

(with uselang=en that's: Revision as of 00:40, 13 December 2002 )

Arguably we should be more consistent, but the information is there.

Making the scope of the bug wider, it appears it's not just on old edits (I thought so), the timestamp is not shown in in the diff-header on any new page creation.

Just in case it's not clear what I mean with "timestamp in diff", I mean the blue-linked "Revision as of 20:41, 23 October 2010 (edit)" on top of the diff-column.

sumanah wrote:

Poking our UI folk with the "design" keyword to see if perhaps there's anything else we should do as long as we're adding the "originally created on..." date in blue at the top.

Either I'm misunderstanding something or this magically fixed itself. Grepping mediawiki/core for the bug number, or for timestamp && invisible, yields nothing.

(WORKSFORME.)