I check my stats every now and then, up until about a month ago, a bot named "Googlebot" – Google's main crawler, naturally, would make frequent visits, and so my pages were updated in the index.

Nowadays, I'm only seeing the "Mediapartners-Google" bot (responsible for determining which ads to put on a page), is it possible that the two merged?

I am positive that my site has been crawled and updated the last month, I just remade my design, and Google's index has it.

This might answer your question:
blogoscoped.com/archive/2006-0 ...