Although those issues still haven't been answered to their full extent I really can't be bothered to fill another thread up with 5 pages of useless answering back. So, just to quote the last part:
I still see no good reason why this cannot be added besides the "it's too IM-like" complaint.
Firstly, I still see no reason why it should
be incorporated just a bunch of reasons how it could
be. Secondly, the final paragraph of the post I referred you to mentions nothing of an IM client. The final paragraph contains a reason as to why I see little or no point in having this dictionary.
TBH, if it was included (provided it was off by default) I wouldn't care a great deal I just don't think such a thing belongs in an IRC client. If the original argument is taken, that being "I'm sick of correcting typos", as I've said, a spell checker isn't going to help any.