@pvcooper and aorlinksy:
It's just. not. that. simple.
http://forums.appleinsider.com/showthread.php?s=&threadid=121142
Key point being: "the Samba team has moved active development of the project to the more strict GPLv3 license, which prevents Apple from realistically using the software commercially"
Bash Jobs or the Apple engineers all you want, they made a decision for very real reasons, and probably would have been far happier to be able to offer the latest Samba instead, less work for Apple's OS X Server team :-)
So they had to go with something else.
The lack of support for NT-style domains is understandable. I wish it were otherwise too, but at this point it would be hard to envision moving anyone *away* from Windows 2003 server (for example) to OS X Server, and keeping XP machines for the long haul.
If you have access to any pre-lion hardware (ie: Lion not required, as with the latest Minis), continue to use it with 10.6 server and plan accordingly.