Registration is so YOU can track your progress. There are no nefarious or unscrupulous purposes behind it.
You will be contacted occassionally with progress reports (and can opt-out if you wish). But that is the only way in which your email address is used.
As you beef-up your Vim Vigor you can also earn some Coder Cred!
It was a highly requested feature and quite a lot of fun to build.
Thank you for your support of Vim-A-Min