It's a little more complex than that. There are two separate things happening here that happen to dovetail together. Let me see if I can clarify them.
The argument that Gene Simmons makes is that as a Rock music as a viable economic opportunity for up and coming musicians is "dead." Now there are many things people can say about Simmons, much of it not good, but he certainly knows how to make being a musician profitable. His sentiment isn't unique either as I've hear many "classic" rock/metal musicians say that if they would never would have tried to be musicians in today's markets. Rob Flynn has made his feelings about how rock bands are treated these days well known and Greg Christian of Testament recently explained that at the end of the year he barely clears $35k, which is about what I make, I'm terribly underpaid, and his job is WAY harder than mine. There are bands with as much major support as you can get these days, that aren't doing "bad" things to waste money on the road, that can tour for a year straight just to break even. So I guess the click-bait headline "Rock is dead" isn't as accurate as "Rock Stars are Dead." The days of any rock musician buying multiple sports cars, mansions, and having endless supplies of women are dead. Top Ramen isn't just for struggling bands anymore.
The music of "rock" is, of course, not truly dead, just as Big Band isn't really dead. But neither are where they were at one point either. However the "rock" that is acceptable for modern radio stations, late night TV shows, and what's left of MTV, are rock in the loosest sense in that they have at least one guy with a guitar and no backup dancers. The Urban Outfitters employee picks, hipster-chow that was mentioned earlier are to bands like Mastodon, Behemoth, Black Label Society, Crowbar and Opeth (all of which have had home run releases this year) as camomile tea is to a Doppelbock or Islay Scotch. Sure they are both beverages, but....
Rock that pushes buttons, makes people think, challenges authority in a meaningful way, or slams the status quo has been marginalized; so to say that its "dead" isn't completely accurate in this context either, but it certainly has been muzzled and neutered. Which brings me to the point you made about "What does clothing have to do with music anyway?" With the actual notes put on a CD, absolutely nothing. But Rock is more than that isn't it? Even from its earliest incarnations, where would Rock be without Elvis' hips and the Beatles shaggy hair? Its about attitude and emotion, its about giving the world the finger. I didn't care for glam/hair/butt rock so I'm glad its gone, and despite its questionable taste I'll take fringed leotards or spiked leather as being emblematic of rock over the high school math teacher or underfed, over manicured shim looks that are prevalent now. Its not the look as much as the weak, submissive, non-threatening attitude it represents.
I'm sure I'll get flamed for this, but $%&# it. Why? Because not giving two @$%s is rock \m/
