If they don't bowl well, they just aren't a very good all-rounder. Your definition of an all-rounder is totally warped really. According to you, someone who is especially good at either batting or bowling can't be an all-rounder.
So Andrew Flintoff isn't an all-rounder because his batting is average and his bowling is exceptional. Kallis isn't an all-rounder because his batting is exceptional and his bowling is average. Pollock isn't an all-rounder for the same reason as Flintoff, and Watson isn't for the same reason as Kallis. Who the hell IS an all-rounder then, aside from Ian Botham from 1978-1983?
Oh, that's right, Tom Moody, who was a mediocre batsman and a mediocre bowler, but at least he was equally mediocre at both.
An all-rounder is someone who is picked in the team to both bat and bowl, simple as that. Mark Waugh wasn't an all-rounder because even though he bowled, he was picked as a batsman, and only bowled occasionally. Andrew Symonds (in ODIs) is an all-rounder because he is picked both to bat and to bowl a significant number of overs in every game. Andrew Flintoff is the same.