Okay, mythbusters.
During the rain I've done a bit of research.
Ambrose has indeed played quite a few innings as a List A opener - in fact he played as a specialist batsman in that role quite often early on. He's done it twenty times in total. Here's the catch though - he hasn't done it since 2004. Why? Well, he wasn't very good at it. He hasn't scored a half century opening since 2002 - which itself was only against Buckinghamshire - and his stats in that position are as follows:
527 runs in 20 innings @
26.35, SR: 52.70; 4 half centuries; HS: 95
Given Ambrose hasn't done the job in four years and he hasn't done it with any success at all in six years, I think it'd be fair to say that Mustard is much better credentialed in that position based purely on the good 2007 he had batting there, but I'll go through all of his 95 games as well if you really insist.
Really, I'm not advocating Mustard by any stretch of the imagination. I quite like Ambrose and I'm backing his selection. I just thought it was a slightly odd time to drop Mustard, especially given the fact that it changed the balance in such a way that ADM was dropped for Luke Wright. I suppose Mustard's poor domestic form played a large part in that.
Slightly off topic, too, but looking at the OD innings Ambrose has played, I'm not convinced he'll be too effective at #7 unless England lose four or five early wickets. He's not a finisher. Best of luck to him, however. He may not suit the roles open for English wicket keepers at the moment but I'd certainly back him to adapt to more different situations Mustard or even Prior with the bat and his glovework looks leagues above both.