If they’d called it Left 4 Dead ODST instead of Left 4 Dead 2, nobody would have had a problem with it.
I think L4D ODST might violate some kind of acronym law somewhere :)
If nothing else it might get GLaDOS sniffing around, which can only lead to Bad Things, such as science being done.
Hark, a Dresden Codak reference?
Mmm… science being done.