Sony or anyone else would *never* put 40" 1080p HDTVs in all demo units. That's absolutely ludicrous.
It will be the S-Series or even the newer cheaper models, the U-series. 720p units. And it will be 26". Imagine playing on a 40" screen at the distance we usually play from at demo units. Besides, Sony won't be making 1080p TVs for quite some time, if ever.
I do expect to see some special demo units though, probably from very dedicated shop managers, with a nice Bravia X or W-series playing PS3 games.
Heck, i fully expect Sony Centres and other HDTV sellers to have their X and W series Bravias plugged to some PS3s. But that will be more to sell the TVs than the PS3s.