Yeah I think that is essentially true if we ignore the injury issue but I would put it down more to the lack of alternatives than any confidence of the current set-up.
"Lack of alternatives" is often a deliberately negative way of looking at "the best players are currently in there". Apart from the fact that the latter is just about all any cricket supporter has any remote right to ask of selectors, the instance where you can look at the seven best players to bat in the top seven and say that, in a Test starting tomorrow, you could have reasonable confidence in them all is very rare - for England or anyone else. Even West Indies between 1976 and 1986 and Australia between 1989 and 2006/07 (two of the best sides the game has seen, which current-England are not remotely close to being) had such a thing only for a season at a time, absolute maximum.
And BTW, currently England have in the way of batting alternatives Carberry, Shah and Joyce (and, maybe, whisper it, Morgan). None of whom are write-offs with no realistic chance of Test success - if any was brought in in place of one of the top seven tomorrow I would believe it possible that they could succeed. You can never, ever know with an untried player, but all of them have something going for them.
There has in recent times normally been a player injured (often Vaughan) who it was assumed would come back in when fit. That is obviously not the case right now but it is certainly worth pointing that Bell (reintroduction in his case of course) and Trott are recent additions and are not many bad scores away from coming under pressure.
No player, ever, is more than 3-4 bad scores away from coming under scrutiny - more so these days than ever. The point I'm making is that this is a rare occasion when I feel genuinely confident that there is no undue prospect of such a thing happening in the immediate future to any of the England top seven. No-one, ever, knows with any real conviction what is coming - players go off-the-boil, terminally and temporarily, for no apparant reason (or due to totally unforeseen circumstances) with considerable regularity. But such things can only be dealt with when they happen - they are different to when there is a genuine "gap" in a side.
Personally I think all of the England top seven have demonstrated that they are capable of playing the role currently asked of them to Test standard - Strauss and Pietersen more than the rest, yes, but at just about any point in the last 18 years I've always looked at the side in the most recently concluded Test and there's been someone in the top seven who I know is, in the immediate future, less likely than more to perform - or else someone I know could be axed next game without any serious "WTF?" complaints.