There's no question that they will be able to make them faster, I'm just asking if there will be any NON-GAMING reason to upgrade from a 5ghz to a 10 ghz. With cars, they could make 800 hp sedans if they wanted to, it's just not necessary. I think the avg HP of cars in America a couple decades ago (that whole "muscle car" phase) was higher than it is today. So anyway, if you take away gaming reasons, why will some random non-gamer need to spend $2000 to upgrade from a 5ghz to 10ghz? Is Microsoft Word 2007 too slow? Can they not get their video emails? I think that 10 years from now people will have 2 main devices: a normal PC that won't need to be that fast to do homework, email, internet, burn DVDs, etc. And then there will be set-top boxes hooked to the TV for video phones, web-TV (won't have to go to Blockbuster) and gaming. Some of these things might be 10ghz, but they won't be PCs.
Now I'm starting to babble, but PCs will probably always be faster because it won't cost more to make a 10ghz than a 5ghz. But still, I think there will be little reason to upgrade in a few years.