Let's count the number of different 360 configurations, shall we?
1. 360 with 20GB HDD
2. 360 with 120GB HDD
3. 360 with no HDD
4. 360 with any of the above and HD-DVD add-on (deceased)
5. And now... 360 with ??GB HDD and BD-ROM drive
This doesn't even account for differences in CPU die, etc! In the meantime developers are stuck designing for the LCD (least common denominator, not liquid crystal display!) so having all the extra stuff makes no difference in your games. Thanks MS, but I'll pass and get a PS3 with my HDTV.