I have heard people complain how vegas didnt feel to like vegas because it was very empty with few people in giant casino rooms.

But does have anything to do with the lag you get when going into these places? I went into a casino filled with around 10 to 20 people and the framerate went down to like 3 or 10 pics a second. So could this be why they didnt put to much stuff in vegas because people wouldnt even be able to even get past the loading screen when entering.

Nah, It's not that. If Fallout 3 could put up with a huge robot getting bombed to crap, I think 20 people can fit in a room.

Sure, I did that level in fallout 3 on ultra graphics but I have turned graphics down to low and tested and it still lags the hell in big rooms with lots of people

especially with combat

There is a hardware driver problem on PC where you get massive slowdowns around NPCs...you could be having that....

Yeah, that seems like the problem

I can watch 50 mini nukes go off but 5 NPCs attacking lags the hell outta everything

if you know a way to fix this let me know

its a very simple fan made fix until either Obsidian or the Video card comapnies fix the problem:
http://www.gamesas.com/index.php?/topic/1123822-potential-fix-for-npc-slowdown/

Does that fix actually increase the number of NPCs in the casinos?

I mean it's just silly in my game. The Atomic Wrangler has 0 customers, and all the major casinos have like 2....

No, that is a fix for people that are getting the major slowdowns around NPCs.