[tlianza]

#2 isn't solved with a CDN since you'd always hotlink a specific version - the version you tested your code with.

The main reason I think isn't even really #1 (cost) but a general assumption that CDNs are faster than your servers, and the chance that if multiple sites are sharing one of these CDNs, you actually have first-time users who can visit your site a bit faster because they already have that resource cached.

[Zikes]

Some CDNs like Google's will let you specify just the major version, so in the case of jQuery it would serve 1.<latest> or 2.<latest>.

Generally undesirable in a production environment, though.