I would be very interested if you could explain what you mean. ;)
C doesn't require you to buy another server to handle more than 10k concurrent connections. So that contradicts the title, right?
But, you can of course handle more than 10k concurrent on the jvm using the NIO stuff.
Imagine if you have a giant datacenter like google, and heat and power are a serious problem. Accomplishing a task with fewer servers is a serious win.