Here is my problem, why some people care so much about providing an infinite way for people to subscribe to their feed? While just 1 way would be enough.
Let's start by saying that all Feed reader software can support the latest Atom and RSS technology. Now, you have Flickr, for example that happily provides you with the following formats for you to subscribe:
RSS 2.0
Atom 1.0
RSS 0.91
RSS 0.92
RSS 1.0
Really? Couldn't they make a decision? Anyone using RSS 0.91 or 0.92 out there?
Technically, I see no issue with doing that, but it causes a very bad user experience. Take for example this blog that I just subscribe: Matt Cutts: Gadgets, Google, and SEO. Very cool content, but why does Matt provides 3 different feed formats? Couldn't he stick to RSS 2.0 or Atom 1.0? That would be more than enough.
My sites only support RSS 2.0. Never, ever, anyone complained about the lack of Atom.
For Matt, things are a little worse. Look at a screenshot of when I subscribed to his blog on Bloglines -- 13 choices! Not a nice picture for a regular user to choose from ("What if I make a mistake?", "What is the best choice?"):
And the real question everyone is afraid to ask for fear of looking stupid... DOES it matter which one I sign up for???
P.S. 13 is amazing... I think the most I've seen is 8. And I just sign up for the one that either has 1) the most subscribers or 2) looks like the simplest URL.