I dont want them to. They will win handily without it. As proven many times in the past people buy for percieved Value not just sheer price.
If anything this works against MS. If someone wanted a PS4 it is still the same price they were already planning on paying. If someone wanted an XB1 they will be happy to pay less.
Also later adopters have to notice it is 150 bucks cheaper now than 1 year ago, many will assume waiting until next Cmas will yield similiar results (price is falling so fast people who actually carea about 50 bucks will wait on future price drops)]
I do think the gap will be narrower than it would have been without the pricecut but I expect a pretty good ass whooping by the PS4.
In the past the consoles that go "bargin bin" dont turn it around. I dont see this changing. Gamecube was like 1/2 the price of the PS2 for a while even though it had more powerful hardware and it made almost no difference.
End of 2009 Predictions (Set, January 1st 2009)
Wii- 72 million 3rd Year Peak, better slate of releases
360- 37 million Should trend down slightly after 3rd year peak
PS3- 29 million Sales should pick up next year, 3rd year peak and price cut