Why does Google omit search results?

[globay]

When I search for "site:www.mysitename.com keyword" Google shows just 2 results out of about 300. Down below it says

"In order to show you the most relevant results, we have omitted some entries very similar to the 2 already displayed. If you like, you can repeat the search with the omitted results included."

The first result is mysitename.com/, the second is mysitename.com/sitemap.html.

Why does Google omit the rest of the search results?

My site is written in PHP using the URL-Rewriting Tecnique to creating virtual folders (mysitename.com/folder1/folder2/folder3/). Does Google notice that there is no real page in the folder? Or is it that Google does not notice the Unique Content (Top, Bottom and Menu, which make up a lot of the source code are the same on every page)?

Thanks,

globay

[ciml]

I think you're just seeing Google's domain clustering. It can be annoying to get the same site many times for a search (as happens on other engines). When you repeat the search with &filter=0 the results are unclustered.