Here's a theoretical situation for the release of the next gen.
Wii2 - late 2011/Early 2012
720 Early 2012
PS4 Late 2012
Which fairly closely mimicks the start of the Wii gen, with Nintendo launching a bit earlier.
Furthermore, we are assuming that the Wii2 and 720 will mimick the Wii and 360 in games lineup, target audience, feature priorities and power relative to what is around. Now lets assume the PS4 mimicks the PS3 in being very expensive, but making up for it with it's value, as it seems may happen from http://gamrconnect.vgchartz.com/thread.php?id=126943. It will of course be a huge jump in power over the PS3, perhaps designed for 1080p 60 fps in 3D, and its games don't display well on 2D televisions.
Lets say the prices of all of them are about the same as their predecessors, adjusting for inflation
Wii2 - $300
720 $400/450
PS4 $700
What do you reckon would happen?
P.S. Take all the info in the OP as assumptions, I am not asking you if you think this will occur, I am asking what it would lead to if it did.