In Google's S1 filing, the number one principle is: "DON'T BE EVIL".
Yet you have punished users by deciding to generate only Atom feeds for free Google Blogger blogs.
I believe this is evil for users. Why?
Well, despite what is written at AtomEnabled.org, Atom is not a standard and it's not even in the process of becoming a standard. It is also incomplete.
I like the people behind Atom. I believe Sam Ruby and the rest of the Atom folks have the best intentions and the final Atom standard will be a boon for the blog community and software companies.
I can understand why you implemented Atom for Blogger. In a word: forward motion.
But since it's easy to generate RSS as well as Atom (if you have the time and resources of a big company like Google), why don't you generate both?
To encourage users to move from RSS to Atom, you could set up the RSS feeds to have less features (e.g. excerpts instead of full text ).
Not generating RSS in addition to Atom feeds, punishes users who don't have the expertise or the permission to install Atom compatible software or to upgrade to Atom compatible software. It also punishes developers who don't have the time or resources to track a moving 'not even in the process of becoming a standard' standard.
I beg you to reconsider your decision.