[seo4china]

It is not because you don't see other extensions on top that you can conclude that they matter less. Think about it, when you register for a domain which one would you look for? A dot com obviously. Dot com are the most used extension and obviously they take most of the top spots. Probably eight or nine out of all the domain registered are dot coms. But if someone was to register a dot net or dot org, and the dot com owner doesn't use or optimize his site, the dot net or dot org will be far ahead of the dot com.

We have many sites which are dot net, dot cn (for China) which are better ranked than the dot com.

The only time that an extension really matters would be on a country-specific level, for instance .co.uk in UK, .au in Australia or .cn in China, when searches are conducted from those specific countries the search engines may consider them more relevant than generic extensions.