Well, you can certainly make a lot of money in a band with out anything about an average amount of musical skill, as long as you have skill in marketing, but I don't think it's fair to make the blanket statement about this kind of a thing. It really would depend on the band, and on the person. The only generalization I would make about it would be that in a band, in general, you don't have to worry as much about group organization; there are simply less instruments being played, and usually less than half a dozen guys, whereas in an orchestra you would have much more than that. But even then, it's not terribly hard to keep time once everyone learns to hit their cues and such.
You also have to remember that music, even bad music, is art. Bad music is just bad art. So while technical skill is important and deserves respect, it isn't all there is to it.
This also applies to rap or hip hop, but that is actually not necessarily so much music as it is poetry and beats. And there is skill that goes into beat arrangement and lyrical work, but a lot of popular rap is just shit. Write about gettin' money and having a bunch of shit and talk about it over a lame-ass beat that sounds like something that a 14-year-old would tap on their desk with a pencil. Get millions of dollars for it.
sigh.