How often exactly was he picked because of his batting, though?
It has been much publicised that this was the reason for his selection in the 2006-07 Ashes series (and although anyone who saw the tour matches will actually tell you otherwise - ie. how Panesar was looking completely innocuous and how Giles was actually bowling quite well - I'll concede it as a truth for the sake of argument), but how often other than that was it true?
AFAIK, he was selected, for the most part anyway, because he was England's best spinner at the time. He was never consistently outperformed by any spinners in English first class cricket during his test career to my knowledge, and those who called for his head generally wanted another batsman or another fast bowler to take his place.
Secondly, this business of "bowlers picked for their batting" became a neccessary evil the day Alec Stewart retired. England locked themselves into picking a batsman - that is, someone selected in a specialist batsman's position - for his bowling: Andrew Flintoff. Flintoff has never in his test career ever been a justified selection in the England test team on his batting alone, so if England were to persist with him batting 6, a counter-balancing player at 8 was required. All the talk of Giles balancing the side all those years wasn't just a Fletcheristic idea focused on multi-skilled players - it was simply common sense once England had decided to pick only 5 batsmen.
I was never a fan of Giles, but his role in balancing the side was often a key one, and the quality of his bowling has been far-too-often played down simply because he can bat a bit.