You usually have to agree to some EULA. It's part of the contract. Second q depends on whether you could have known what's in the EULA before you bought it. They're not separate things. There is no such thing as 'buying' and 'agreeing to a licence' or anything like that. A 'licence' is just a contract: party A pays $X to party B, in exchange for which party B lets party A copy its IP, under a given set of conditions. 'pay for the copy but not for the licence' is a grammatically correct sentence but meaningless, like when I'd say 'I punch this wall red with my horse'. Copyright is about 'copying', so if that's what you mean by 'distributors', then yes. But so do 'EULA's' and all other IP-related contracts (usually called 'licences').

As to your last question: yes there is, people have written dozens of book about it. Your local university probably has a bunch of them in their library. If you're asking about a website where you can read in a few paragraphs the complete legal context with definitive answers to questions about general cases (i.e., no 'it depends' allowed) - then no, such a thing does not exist. Look at it this way: if a novice programmer goes onto LKML and says 'hey guys, I want to write an OS, can someone point me to an overview' - then at best he'd be pointed to some high-level overview Wikipedia pages, but most likely, people would snicker and press 'delete' (well actually he'd probably receive a bunch of abuse on how he should get off the list, but that's specific to the example I chose...)

FWIW, I did read a bunch of book like the ones I mentioned above when I was writing a paper on a EULA-related topic during my law degree, and as a result I don't make any blanket statements about the topic any more.