The tag is obviously the better choice since it can block any kind of adult content. Whereas .xxx is for porn only. Anyone who supports .xxx for the protection of children is also going to need to support .violence, .language, .gross, etc...

Technically ISP's could offer family safe internet right now. Take the software that parents are apparently to incompetent to install and just run requests through it at the ISP level. Every mother in America would want it, and her husband will quietly agree while biting his tongue. No porn. No p2p. No reason to upgrade to faster services. That's why they don't offer it.