Third-Party Cookies

I was planning to ask if "Accept third-party cookies" could be disabled by default in Firefox, as it's mostly used by advertising companies for tracking users across sites. It seems that some applications rely on it, though: two long-standing problems (no "Play" icon in the BBC iPlayer on iPhone; extension for Songbird won't sign in) have occurred when this option is disabled and third-party cookies are prevented from being stored.

Is this bad practice by the applications that rely on third-party cookies, or are we stuck with having to allow cookies from third-parties (or at least adding exceptions for a few domains)?