It can be controversial, but that doesn't mean it's any exception to the rule. And South Park, being a TV show rather than a game (even FO3) gets alot more exposure, and has been firmly in the public eye for over 10 years. What about homosixuals? Why wouldn't they be portrayed? Did homosixuality burn in the flames of 2077? And where do handicapped come into it? o_O All I know is, Fallout wouldn't portray such stereotypes in such a demeaning manner as to a show like South Park. see http://southpark.wikia.com/wiki/Mr._Slave for a less than honest potrayal of homosixuality in South Park. Fallout isn't into demeaning stereotypes. If Mormonism is included, I'm sure it wouldn't be anything but an honest look into such a community.
Southpark is a tv show. Although episodes of TV shows do involve some risk they don't equate to the sort of financial risk a mainstream game entails. Let's look at worst case here. The game is released with the Mormon content, and using the FO3 numbers, ~4.7M copies are distributed for the rollout. It's going to cost less to produce F:NV, but it's still going to be millions, probably tens of millions. Despite what the developers think is a reasonable and fair, perhaps even flattering depiction of Mormons, the Mormons do become offended, and decide to put their foot down (they do this on rare occasion...they are more inclined to let things be).
Most Mormons aren't likely to Play Fallout to start with, so a boycott in itself might not have muc direct effect. Indirectly, however, should the boycott be picked up and amplified by some of the more militant religious groups here in the US, along with people like Fox New and the rest of the "Culture Warrior" mouthpieces, the game could be in real trouble. Something similar happened to Magic Compass, although that movie was definitely ant religious generally.
Point is, this game, or any game, represents a long term and substantial investment. The money ahs alrady been used by the time the game releases, and some set number of units must be sold to recoup costs and build profit for teh company and it's investors. No one is going to want to take any excessive risk to that revenue.
It's easy to argue that it won't happen, and perhaps it probably won't. If it does, the impact may be minimal. But there's a lot of probably and maybes there, and it all revolves around the reactions of a group (Mormons) whose actions are not controlled by the investors. That makes it a gamble, and that's a lot of money.
I get that folks want it in there...they think it will make the game more like VB would ahve been, but we aren't putting up the money for this, and we aren't calling the shots. Beth might decide to risk something like this, but it makes absolutly no business sense. Something like this could wreck the economic viability of the project, and perhaps even the franchise, and the company, from a PR point of view. It's just too risky.