Yeah, I haven't read anywhere where one is better than the other on a standard config device. The problems arise during the flashing (upgrading) of custom ROMs that are created (cooked) in kitchens. The most technical explanation I've seen is in this sticky (post1):
http://forum.ppcgeeks.com/showthread.php?t=7820
When you start using the kitchens, there are alot of extra programs that you can include with the OS to create the custom ROM. Most people include way too many and the ROM becomes too big. Alot of flashing problems, stuck at bootloader, stuck at splash screen, stuck at white screen, etc. I've read that during compilation, the beginning files are overwritten. So I guess you could say that the BL1.xx have an advantage here. However, the downside is the 1.xx bootloaders are not Vista/WMDC compatible (you use Activesync/WMDC to transfer the ROM to the 6700) but there are workarounds for that as well.
So, in laymans terms:
1.xx more ROM space, less program space
2.xx less ROM space , more program space
I can see why they did it as once the ROM is loaded, any extra space can't be used anymore so it is wasted. Simple optimization. If you don't flash, no worry, as long as you don't run out of program space. Hope this helps.