Last xmas, 360 was in short supply...and luanch systems are usually pick up by hardcore gamers that is willing to pay for higher price. Once that is oout of the way, regardless if PS3 launch this xmas or not, MS needs to capture non-hardcore gamers.
Non-hardcore gamers has the option of getting a 360 at a relatively cheaper price without all the *extra stuff*. Non-hardcore gamers with interests in video have the option of picking up a HD-DVD addon. What they're trying to do is capitalize on the holiday demands. By having more options and attracting non-hardcore, they can expand their base. PS3 is in no position to steal any sales from MS, so why should they be in panic mode?
Now, with PS3 in limited supply, it means some people will not want to hold out...and might opt for a 360 in place of PS3. That's just an extra bonus. To really capture PS3 ******s, they have to an excellent line of games, which IMO they're doing just fine. I'm sure they're spending a bit of cash to secure it, but hey they can afford it.