Gilchrist might've been got out with the round-the-wicket ploy a few times since Lord's 2005, but if it really was that simple he'd not have averaged 60 or close ITFP. No, he's played more than his share of poor strokes since Lord's 2005, too.
I watched most of the Gilchrist innings in 2003\04 and early 2004\05, too, and he quite clearly played far more poor strokes than he had done in most of the 1999\2000-2003 period. Maybe (and only maybe) that had to do with bowlers bowling better at him - and also, of course, due to the fact that he faced some quality spin in the period, something he did little of in the 1999\2000-2003 time.
Purely and simply, I'd say Gilchrist's style of play was always likely to get him into some trouble - I've always said that if he'd played in a time of better bowling and better catching, he'd not have averaged 60 as he did at first, probably more like 35-40.