: If this is the case, why?
Probably easiest answer I have for you is, well, it's Marathon - it's not going to look like Unreal 8 or whatever, minor graphics upgrades like that don't really chage it's core Marathon'ness - and for the extra time and effort it'd take to produce them, personally, I'd rather the dev's focus on finishing the core game for release first - release that other stuff later, if they want.
I'd hate to think if Rubicon had been delayed, what, 4 years ago, not even released yet, just to implement stuff like that -> Rubicon X.
Not to say I don't appreciate the stuff, I do, hugely, but honestly... *shrug* 'thon is 'thon, no matter how it looks.