All you have to do is look at the sales prices. .com is now clearly the champion. It is highly unlikely that it will ever be dethroned. My principle business is at
www.hiosilver.com . I don't even care who, if anyone, buys the .net, or .us or .de. This is not an online business.
A lot of people settle for a .net or .biz or a ccTLD because that is what is available. When they succeed, most want the .com, if they can get it. I have sold .com and .net names to German companies that have been operating for some time under their .de. They KNOW that without the .com, they are losing traffic.
Had I not been able to get PPCIncome.com, I would have settled for the .net or whatever, but I would always be looking for a chance to get the .com. I have it, so I really don't care about the other extensions.
Pick up a US airline magazine the next time you fly. Check out the ads. How many have domain names? How many have .com domain names? How many have .US domain names? .net? etc. These are real companies with a real need for the best domain they can get. Clearly, if a business in Germany wants to focus on Germany, they can do fine (maybe better) with the .de. However, as soon as they want to get US business (or possibly even other countries), they will try to acquire the .com.
Anyone thinking that .us or .de or .biz or whatever will dethrone .com is just doing wishfull thinking because they own "better" domains in these other TLD's.
With so many alternatives, of course the .com slice of the pie will keep shrinking as a %. The more alternatives there are, the more confusion and the more valuable .com becomes. This is a big part of the absurdity of those advocating lots of new TLD's. With so many country codes, ICANN should forget about new generic TLD's.