about the SEO method of second-level domain name

[Guest]

I have some questions with SEO method about second-level domain name. Why Google indexed thesecond-level domain name more faster than the URL who include the "www"?

For example, my friends tell me the http://www.tradetuber.com is a large global online B2B marketplace. They have more second-level domian name like the jawcrusher.tradetuber.com, but it's content is similar to http://www.tradetuber.com/jawcrusher/jawcrusher.htm.

Why Google indexed the front one more faster? What's the difference between them?