What difference does it make whether the URL of a page includes the "www" part or not? Does that hamper the Google Spider's crawling process?

Just to make it clearer, I mean the difference between
http://www.techzonez.com and http://techzonez.com

The reason I'm asking is because I've recently added a few pages to my personal site. I browsed through these newly added pages to check everything was fine. But after a certain point, the "www" would no longer appear in the address bar (although I do not remember doing anything differently when I created those web pages).

After a couple weeks, when I went to check if Google had indexed my new pages, I found that it had stopped indexing the pages from the point where the "www" no longer appeared in the URLs. Is it a coincidence or should I wait longer and see what happens?

Even if it's no problem, can you tell me how to get back the "www" into all of my pages' URLs? I want it to be consistent throughout the site.