Why release a new version and then digress from the already established functionality?
I suppose it was done in order for scripters to get aquainted with pawn (for those who had no experience with SA:MP's scripting). Also, while having "digressed" functionality (which can be seen only in few functions), pawn features more "integrated" scripting solution - you don't have to connect scripts to server, they can't suddenly "timeout" from etc.
Plus, it is safe to say that the upcoming release (which is, I repeat yet again, uses pawn) is absolutely superior to mrc.
Providing one and only one scripting method on the 'official' wiki, when there are more useful ones out there, just seems ignorant.
1) I don't think you know the basics of wikis. They are not "big readmes", written by devs/testers, they are free-to-edit databases to which anyone can contribute.
2) As a result of above, content greatly depends on contributors. I, as one of the biggest contributors, had only enough knowledge/will/time to fill in pawn information. You are free to add mrc/squirrel information if you feel it's missing.
3) There is an unofficial wiki, hosted by VRocker, which covers mrc and squirrel scripting. It can be found here ->
http://liberty-unleashed.co.uk/VCWiki/Main_Page