> Then why did I get this message from WordPress.com?
excellent question!
"We hope you dig your new weblog. If you have any questions or comments, please let us know!" at http://wordpress.com/contact-support/
I suppose you're happy user of the web application WordPress downloaded from "community owned" site at wordpress.org, correct?
you see, Akismet is commercial service which is free for personal use. regardless of its usage terms everyone has to register a user account on the wordpress.com (thus increasing its userbase) just get a so call 'API key', which activates plugin said.
forget that spam was ever a problem, forget about some legit comments too.