It's a decent stopgap, but a bad primary effort. If you get big enough to notice, you end up offering basically two things to the people running those sites:

1) Do work and support RSS or

2) Do nothing and we do it for you for free

Which do you think they'll choose? And then you're stuck running a big clearinghouse for RSS feeds, with fund-raising problems, users griping at you because some feed isn't perfect, etc.

Myself, I've had decent success just asking if someone could please add an RSS feed to their site the few times it's come up. It's apparently easy to do in many CMS's that don't do it by default.

I'm pretty sure Feedly does this (about as well as it can be done).