Why do namecoins have any value? Many Bitcoin mining pools offer merged mining with Namecoin, and there are places where one can buy and sell BTC for NMC and the other way around.
But, why would anyone want to own NMC? As far as I understand, browsing dot-bit domains doesn't require owning NMC.
Namecoins are used to register .bit domains:

http://dot-bit.org/HowToRegisterAndConfigureBitDomains

They're also bought and sold by speculators, but DNS registration is their original purpose.