Everyone fucks things up from time to time (except Tester, probably) - it's then a crap shoot on the thing you fuck up. Get lucky and it's rounding off a bolt. Unlucky and you've ruined a £200 postmount fork.
From a consumer's perspective flatmount and IS are both better standards.
Actually, having seen how many threads there have been on Singletrack, asking about fitting a helicoil to their brake mount...