Mainly to prevent abuse. There are several reasons people may go back and edit their posts long after 2 hours, for example, if a moderator has edited their post they may be watched for a couple of hours...if the edit time is not there, they could just edit their post to its previous abusive form much later on. Secondly, people could edit posts and make certain replies/users look irrelevant or stupid, and then claim they never edited their post in the first place...no way for us to tell.
To be perfectly honest, Khaled has been fixing bugs in mIRC over a decade. Thus far there has been no need to consolidate all bug reports into one thread to make it easier for him (or the community), so unless Khaled himself makes a sticky thread requesting such behaviour, I also feel it unnecessary.
Naturally though, everyone's efforts in reporting bugs, particularly for this version as clearly many changes were made, are appreciated