Many people have said "well, if they add achievements, or add LIVE capability, I would pay for it!" Nobody was sure if they would or wouldn't. Trouble is, based on this article, we now know "they won't."
What gave it away for me is the compatability issues list, seen here:
http://www.xbox.com/en-US/games/xboxoriginals/issues.htm
They are all the same as the current backwardscompability problems in the games right now. Fuzion Frenzy will have some lag issues, Fable with audio static, etc...
If they haven't "gotten around" to fixing that stuff (so to speak, of course it's not always 'just that easy'), then it's not likely they've taken the time to add achievements. And it's even LESS likely that they took the time to add Xbox Live multiplayer code and all of that jazz to Halo!
But, still... the ability to download classic Xbox games, at what is a reasonable price... what do you think?
NuAngel