This was obviously an April Fools' joke, Xdebug will continue to stay Open Source and free of charge.
Later today I will be releasing the first Release Candidate of Xdebug 2.1. With regret I have to announce that from this release, I will no longer provide Xdebug as an open source debugger extension. I've noticed that there are other projects making money of Xdebug's success while I only receive donations from a group of awesome supporters.
Xdebug will continue to be available for benefactors on a limited number of platforms that I have access to (Linux 32/64bit and Windows). Please refer to the FAQ for further information.