If they release too soon I think they will actually see smaller sales and hurt their growth.
Wii has made it absolutely clear that having the best specs means nothing regarding selliing the most consoles. PS3 recovery has me thinking that the early release didn't even hurt Sony directly - Sony did that themselves with price point, lack of games and the HD format war. To be clear what I mean is that looking at PS3 sales since price cuts and the games started coming ig Sony had their house in order from the get go they'f probably have caught up with 360 as fast as the Wii did.
If they release too early then they will on;y get the hardcore in US while most likely the broader install base will stick with Wii, PS3 and yes the 360 (unless MS kill it).
With the likely impact on economu over next 2 to 3 years I also reckon that asking consumers to buy another expense console would not go down well vs sticking with the console you have and ploughing the money into games purchases instead.
Try to be reasonable... its easier than you think...
