Unfortunately that will not cover you; The United Kingdom Privacy Laws are respected by that of the United States and all friendly countries, therefore if I choose to have my account deleted from your site for Privacy reasons, you
must comply - However, regarding post content, that is something that you would need to speak to a lawyer about; I as an individual can post it anywhere I choose providing the content is mine, but under Copyright laws you need my permission to post it elsewhere; If you stipulate that by posting it on your site you are taking part-ownership of the content for use on your site, that would cover you, although open you to the issues of bad post content etc...
Its a tricky situation, you'd be best consulting a Lawyer about it, however, as a British citizen, a country on friendly terms with the United States, stating that removing my account is not allowed unfortunately does not make it so; I assume that Privacy Laws in this country will override your rights in this instance
Chris