I recently had 4 tyres fitted for a tenner a corner as well, i actually mentioned to the guy that they were the cheapest by far than anyone else around, highest place quoting £30 per corner to fit a tyre!
I asked him why thats the case and he said its to try stop people from buying cheap online and then just going to tyre placers for fitting as they dont really make any money from it
And that's exactly what's happening. Until all the online tyre retailers cornered the market (including ebay) you used to be able to get a tyre mounted for about five to seven quid, not it's at least double that if not considerably more.
There is a place around the corner from me who will still do them for a tenner each, cash in hand, but they seem to be the exception to the rule round these parts.
I don't see how the size of the wheel comes into it really, it's the same length of time labour wise, you use about the same number of wheel weights and the same amount of air pressure no matter what size wheels you're dealing with. The only issues I can see is the marking of diamond cut alloys being a perennial problem, but many VAG wheels have at least a diamond cut rim so we just can't escape that little issue.
