the problem is your hand, not the phone...
The gap isn't cosmetic, and there (likely) isn't a manufacturing flaw. The issue is that the user's hand can bridge the gap, whether or not the antennae are isolated on the phone (i.e. your hand shorts the circuit).
It's an embarrassing design flaw, and a stupid decision to put it into production when the problem was foreseen earlier, but not the end of the world. If it weren't Apple (or MS), the issue would make the tech pages, but not come close to the front page.
You _can_ hold your phone different(ly) or use a case of some sort , and resolve the major part of the issue (bridging of the circuit), and Apple are right to say that signal attenuation with any phone will always depend on where your hand is in relation to the antenna.
The simplest fix for iPhone 4.01 will be an electrically insulating coating over those metal parts, and no doubt the production line is already gearing up for this.
Fingers crossed there will be a voluntary trade-in scheme for people experiencing issues, and subsequent availability of discounted refurb 4.0 models with the problem (for fanbois like me who would like one, but can't fathom spending that sort of $$ on any phone). For half price I don't have a problem holding my phone diffferently, it could hardly suck worse than my LG.