While Wii continues to dominate overall at the two retailers, though, GTA IV 360 is sitting pretty at the top of the GameStop tree, although on the Amazon.com sales chart Mario Kart Wii has ousted Rockstar's sandbox title this week to take pole.
Wii Fit is the big news in the UK, with the title not being able to appear in Play.com's Bestsellers list due to supply shortages for the second week running.
The game has pushed GTA IV PS3 off the second spot in the Amazon.co.uk charts.
It is also worth noting that whilst Mario Kart Wii comes in fourth place on Amazon.co.uk, Play.com is sold out of this as well, meaning the store's top ten could look rather different if this and Wii Fit were in stock.
By Mike Bowden