But anyway I am pretty sure to have read somewhere that you have a right to delete your account anywhere on the web, and that websites not providing this right are against the European Law
It's not the account itself, only the privacy-sensitive information. For instance, a few weeks ago a dating-cheating site got a lot of publicity because their "premium service" (where you had to pay money to get your information deleted) didn't actually delete things. Under European law (to which that, American, site wasn't subject anyway), they couldn't have charged money; anybody could simply have told them they wanted to use their legal right to require the deletion of personally-identifiable information (such as email addresses and real-world addresses, probably date of birth too, etc.). The remaining stripped and mostly-empty account (possibly still containing non-personally-identifiable information, such as for instance account creation date) would still remain however.
Keep in mind that European law cannot apply to non-European websites (if anybody knows any US politicians: please talk some sense into them; the way it completely and utterly violates the concept of "jurisdiction" and abuses "meh, we'll still get away with it" explains a big part of the current unpopularity of the USA, even among its theoretical allies). In a way, consider yourself a "tourist" when visiting non-EU websites; when you actually go on vacation to the US, EU law doesn't apply either.