Because it would be just as stupid as Google shutting down it's Reader.

I've wanted Tumblr to allow you to subscribe to external rss feeds for a while (I think it did at one point) -- some of he blogs I read are text heavy, some are graphics heavy, etc., and it would be nice to have separate readers optimized for the different types of content. It would be nice to be able to subscribe to "tumblrs" on the tumblr dashboard whether or not they're actually hosted on tumblr.

Reddit's kind of the same thing: it would be nice to have a reader integrated with the discussion.

The dashboard isn't good at telling you whether you've seen a post already and moves much too fast for traditional blogs that post once a day or less to even show up within the first few pages. I don't think Tumblr has the right UI for an RSS reader.

Sure, but there are plenty of light, "pretty" blogs that I'll browse when I have time to kill, and tumblr wouldn't be bad for that. I'm not arguing in favor of Tumblr necessarily, but specialization. I'd love Twitter to have a separate but connected rss reader, for "twitter-like" content, for example. Any of these social network or quasi social network services could offer a customized rss reader - it's like having the best JavaScript "share this page on..." button possible.

Because those of us who are used to of scrolling content from these services, can stay at one place.