The GameCube PS3 comparisons are really tired. The reasons both systems did underwhelming early on are completely diffirent. For the GameCube it was a combination of Nintendo's kiddy image and a lacking of third party support. The PS3's problem is price and not enough first and third party exclusives. A hell of a lot more hardcore gamers are interested in the PS3 right now than were ever interested in the GameCube. The PS3's problems are much more correctable than the GameCube's. Price will come down, and if MGS4, FFXIII, and GT5 all make it out in 2008 watch out.
As for the 40GB version this year I could see it having a solid effect. I definetly see it selling bellow the 360 for the holidays season, but the gap might not be as big as some expect.