I agree with timethief:
Before I came to wp.com, it seems that folk could edit their own comments here. Apparently lots of people took advantage of that, and threads became nonsensical with multiple edits.
Most people can understand text speak (even me most times!) and typos, and still read (even excuse) what a person has typed.
Questions and answers here get picked up by Google very quickly and edits here make problems when it comes to searching these forums.
But as I’m a volunteer without access to the behind the curtain details, perhaps that will be allowed in future…