The rumors are true, from the Robocup Committee itself:

Dear 4-legged RoboCuppers,

I have just received an e-mail from Minoru Asada that Sony announced that
they will stop to produce AIBO by the end of this March. As long as they
have AIBOs, they will sell them. The services such as repairing and parts
exchanges will continue for about 7 years after they stopped the production.

Sony decided to completely withdraw from robotics related activities.

In 2006, we will hold the Four-legged robot league competition as planned.
After that, we have to discuss what we will do (especially the TC).

Best regards

Thomas Röfer

UPDATE:: More, From the Sony Aibo representative, to the Robocup 4legged League mailing list:

Dear all,

As Asada-san sent the email, Sony announced that Sony discontinues
production of AIBO.

Since the beginning, AIBO has grown up with RoboCup. We very much appreciate
all of your understanding and support for AIBO and Sony’s activities. I know
the discussion about a platform in four-legged robot league and appreciate
the decision to use AIBO as the platform for RoboCup 2006. I appreciate to
it and I regret that Sony made this decision though it is your supports.

Personally it is very sad to stop AIBO production, but as Kitano-san
mentioned
it is a new start for next evolution for RoboCup.

I believe your success in RoboCup 2006!!
Thank you.

—- Masahiro