Not a lawyer as well but I'm not sure about this. Let's use the "jQuery served by a CDN" example here: You can easily argue that using jQuery is necessary for your site to function but there is no real benefit to the user by doing this with a CDN when you could just ship jQuery from your own server. AFAIK the benefit of CDNs is largely nullified nowadays by browsers using a different cache for each primary domain anyways, so you can't even really point out a potential benefit for the user (faster load times) here.
