Mark-
Why the hell was this changed? Why was no one told before hand, or even afterward?
Making www.wikipedia.org a multilingual portal has been suggested by many different people ever since the creation of new languages besides English. I point you, for example, to this summary by Elian written in October 2002, where a large number of people favored a multilingual portal:
http://mail.wikipedia.org/pipermail/wikipedia-l/2002-October/024522.html
The change from www.wikipedia.org to en.wikipedia.org was made in part to accommodate any future mulitilingual portal, and if you browse around Meta, you'll find several proposals for such a portal.
Not discriminating in favor of or against any particular widely spoken language is an important part of Wikimedia's mission. The fact that www.wikipedia.org redirected to the English Wikipedia has, for many, been a long-standing violation of this principle.
Partially in response, the English Wikipedia has in the past spent considerable energy on making the other languages more visible on the Main Page. Now that www.wikipedia.org is a portal, we can dare to make en.wikipedia.org a little more English-centric.
Why has the creation of the portal taken so long? Mostly because nobody wanted to make a decision about what the portal would look like. With Tim's solution, which is editable through Meta, the community can work this out over time.
Regards,
Erik