This is expected to be done for two reasons - for one, with the price of the PS3 expected to be magnificent, Microsoft can raise the price of the Xbox 360 and still not be the most expensive console on the market. Secondly for brand purposes if the Xbox 360 is significantly cheaper than the PS3 - up to £100 cheaper, perhaps - then to consumers not as in-the-know as somebody who has been following every inch of these two machines as they have been developed will see the Xbox 360 as an inferior product.
Maybe this means that Microsoft might actually make a profit off of the Xbox 360? One thing is for sure, the consumer sure as hell won't µ