Rio never gets drawn out wide, his reading and organising is too good. Plus he's generally had a more conservative rightback while Vidic has had Evra, and there are miles more natural right-footed wingers than left footed ones. One of Vidic's trademarks is how well he deals with opposition wide players when Evra is caught up the pitch, the fact it happens twice a match at least means he's bound to have once or twice a season where he gets caught out.
You're massively overstating what is actually a relative strength to his game, being 1v1 with a quick winger is going to end badly for you most of the time, Vidic is miles a head of most centerbacks when it comes to that. I even highlighted Vidic as a brilliant example of how to do it right when Smalling was having troubles covering the wide positions.
It's one of the harder things to defend against, Vidic has to do it often so it's not surprising he's beaten once or twice and it's more likely to be Torres than Ricardo Fuller.