Exactamundo!
The creators of the film are in their mid-thirties, I believe, and so are a lot of their fans. Many in this age bracket, who had an extended adolescence (Generation X ex-slackers, and former punkers close to 40 - as Trey Parker describes himself), are settling down, raising familes, and having to deal with life-and-death issues for the first time in their lives.
Given the dreary socialist institutional drivel they've been subjected to during their formative years, anything anti-liberal is new and refreshing to them. Especially, as you point out, when delivered with a sense of humor.
Perhaps, but I'm 48, and both my husband (56) and I loved it! Of course, we still subscribe to Mad Magazine so that might not say a lot about our level of humor maturity ;-).