The PS3 is in plentiful supply in the UK so no-one is going to make any money selling them on ebay.
The Wii on the other hand is back to selling for £250 (£70 over retail) plus on ebay.co.uk which proves that demand is still far outstripping supply.
I'm surprised by those 360 v PS3 Amazon figures. If that's indicative of other retailers then bad news for MS and good news for Sony.