How does Google pick and choose pages?

[komalani]

I've been reading through the forum and trying to find an answer to what is still a nagging question. Why does Google decide to index some pages over others on the same site when the number of internal links etc are the same? It seems like lately it's a matter of first come first served, the first few dozen pages it sees are the ones it will list, everyone else gets bumped.
As an example, PolyPro Big Grocery Tote has been up for weeks and is linked from the front page. I do think it was initially listed but vanished. It's in the sitemap, doesn't seem to have any issues that any other page doesn't have yet it's not appearing even in the supplementals. Is it just a matter of time?

Are there any tools out there for free/pay that will check a page against a basic checklist of "to do/not to do" to make sure I'm not missing something basic?

Thanks