The problem as i see it is that many defenders know what pace he has and therefore take every opportunity to clip his heels [ Ivanovic yesterday being a prime example]. This constant fouling looks like they have been slightly beaten by pace and therefore they get away with quite a bit of this cynical fouling before they are booked].
They realise that, if left, Bale will rampage past them all afternoon.
The problem is that i think Bale anticipates this clipping and almost expects it. Therefore he is reluctant to be as aggressive in his runs as he once was, he is also reluctant to go full pace because he knows what will happen and the faster he is going the harder he will fall [Game against Ars*nal being an example].
What I don't understand is that once he has had the defender booked why don't we feed him more ball and get him to run at the nervy defender even more.
In other words i think he is expecting to be fouled and this is effecting his approach. None of this would be as bad if he was allowed to take the resulting free kicks. Presently we use VDV who is only effective from near the penalty area and Kaboul who is only effective if the wall is poorly positioned. Bale is a known dead ball master, he wins most of the free kicks so he should be given a shot at taking them.