Google Search Confusion

I was gathering some information for my previous hub Startup Resources in Google. I searched with the exact words - startup resources. The number of results displayed was 399,000. Suddenly something stuck me and I was so curious to check the last result possible. I mean I wanted to keep on skipping pages and move till I get exhausted(399,000 results!). But there is something else that happened.

The navigation page did not proceed after 64 pages of search. The information display showed: 631-635 of about 399,000 results. After that the numbered navigation thing itself was not there. I am not able to understand why something happened like this.

So then I tried searching only for the word Startup. The number of results displayed was 42,300,000(Oh my!). But the same thing happened in this case also. Only difference was the search results stopped displaying after moving to 76 pages. The rank of results at that page was only 751-759. And don't forget this is out of 42 million search results. I can't think of any possible answer and I don't have the curiosity now to search for anyother term. If anyone knows, share with me.