My 4.5yr old still has the odd poo issue his jocks. When he does go on his own to the toilet he can competently wipe his own bottom. I do ask if he needs help and can I check, and he says "no I am fine mummy".
I was talking to some Mum's at school a couple of months ago about DS2 and toilet training. One of the Mum's says her 7yr still doesn't wipe his own bottom and she does it, I asked her what he did at school and she said he just doesn't poo at school!
So I suppose it's the old different strokes for different folks thing

ETA: When he does wipe on his own, we go through alot of toilet paper!!