I'd much rather pick someone who's proven that he can bowl consistantly than someone who has shown terrible inconsistancy in County Cricket and is then picked in the England side and continues in that veign, a few good performances aside. Yes Harmison may be a different bowler but many people, myself included, don't really give a damn weather a bowler can bowl 45mph or 90mph as long as they take wickets. Therefor, despite Harmison's 4for (which included 2 gifted wickets thanks to careless strokes and amazing catches), I think many people would rather have Saggers in there simply because he really would struggle to do any worse.
As for your comment on the fact that you "don't want a bowler picked on county wickets", right, then what is the point of having a domestic competition? Didn't Trescothick just start scoring runs for Somerset just before his England call-up?
Anyway, top English wicket taker this series ends up as James Anderson, what a turn-up! Not to be biased to Harmison, even after this 4for, but many English fans I've spoken to would still rather have a Saggers in the team instead of Harmison any day of the week.