The only reason for trainer use[...]
Objection! Use of
only!
As a counterexample, I pretty regularly pull out the memory editor or (if it's convenient) a trainer for games that also have built in cheats. I've done it to the original SC a number of times. It's mostly a matter of convenience; typing in some unwieldy stream of letters every few moments/once per game (may go through quite the number in quick succession while cheating, remember.) versus the one/two button (often in-game) functionality of trainers or the (potentially) persistent effect of the memory editor.
Trainers are usually a lot quicker and more fluid in their cheat activation than anything the developers put into the game itself, at least when there's been any effort at all to implement a decent UI.
So I'd lay bets with you not everyone using them was trying to get around the achievement thing. Some just wanted to type less. Probably other reasons, too. Quite a few probably were trying to get around the achievement system, of course, but that only language gets you in trouble
Rest of conversation I guess doesn't really do anything for me. Won't be buying SC2 anytime this half of the decade (or this decade, period), no real interest in clearing out the HD space to filch it from somewhere. Maybe if I hear about something amazing coming out of the mapmaking stuff and the price went down, I'd fork out some cash, but... eh.
EDIT: Has anything really neat been produced yet?