I know there is onpage and offpage factors but from a standpoint of the search engines.. if you had to sum it up in a sentence, why google ranks one webpage over another what factors would be involved? Is it the other page has more backlinks? Is it the other page has less backlinks but the ones they have come from pages which have high page rank? Is it onpage keyword density? is it good html?
trust, age of the domain, authority of the site, on-page optimization factors, incoming links with appropriate anchor text. that's about everything.
relevancy, in my personal opinion, only plays into trust. if you've got a domain where trust isn't a factor, you can have completely irrelevant incoming anchor text and rank just fine.
so do you think google looks at how long you have bought your domain for i.e 3 years vs someone buying a domain for 1 year and renews it each year?
it's been mentioned in some papers but I doubt it has much of an impact at all, if it has any. the most important factors are those I listed above.
those simply prime the site for ranking, they don't actually get the ranking alone; they just allow it to rank. all of the above (trust, old age of domain, authority) without on-page optimization and the correct incoming anchor text won't rank for a thing.