You are right, there is a continuum of possibilities between pure search and pure recommendation systems.
The difference is in the input data that the search/recommendation engine considers: the input in classic search is only the few words in the query, while a recommendation engine considers some history of your interactions with a site or the internet (and nothing that indicates your intent in this particular instance).
Google, of course, keeps search history for people logged in. But it doesn't seem to affect their relevancy algorithm much, unlike, say, your location and language.
I'd speculate Google Checkout is mostly about gathering data that would allow for meaningful recommendations.
The difference is in the input data that the search/recommendation engine considers: the input in classic search is only the few words in the query, while a recommendation engine considers some history of your interactions with a site or the internet (and nothing that indicates your intent in this particular instance).
Google, of course, keeps search history for people logged in. But it doesn't seem to affect their relevancy algorithm much, unlike, say, your location and language.
I'd speculate Google Checkout is mostly about gathering data that would allow for meaningful recommendations.