There are blogs that only supply a resume or part of the content in the RSS. And the reason, I guess, is that they want you to leave the comfort of your own RSS reader and visit their site and maybe see some ads or who-cares-else what.
Well, FUCK THEM. The best I know are not doing it. Actually the best I know have no ads and have minimalistic web sites (I understand it as only content and unobtrusive navigation buttons/links).... and..... provide outstanding content.
Blogs that do that:
I decided to stop reading them.
Other things that turn me down - copyright footer, a lot of links like "vote for me in ...." and guys that start taking themselves too seriously. For the latter I'm ready to make an exception, because some of them have an amazing style.