With thanks to briosafreak, techradar.com put up an interview with Pete Hines, where he explains why Bethesda prefers to showcase the 360 version of Fallout 3, and why the fun won't stop with Fallout 3.
Here's an excerpt from the Wordpress:
“If you have the PC as your lead machine you have the problem of not knowing what configurations people have, how many gigs of RAM or what graphics card they have,” explained Hines.
“Obviously we are more familiar with the Xbox because we are familiar and the other thing is that the Xbox is much easier to take to tech shows”.
“We can just pop the hard-drive off the Xbox and put it on any machine which is an advantage. Taking the PC or PS3 to these things just isn’t convenient.”[...]
If you want to play the Fallout 3 downloadable content you will need to have an Xbox 360 or a PC.”[...]
“We didn’t buy the Fallout franchise to just do Fallout 3 and then stop”.
You can read the entire article here.