A continuación del dejo el anuncio oficial realizado por Rick Spencer responsable de la decisión (en):
Each release we determine the best default web browser and the best
default search engine for Ubuntu. When choosing the best default search
provider, we consider factors such as user experience, user preferences,
and costs and benefits for Ubuntu and the browsers and other projects
that make up Ubuntu. Up until Ubuntu 9.10 these defaults have always
been Firefox and Google. Earlier in the 10.04 cycle I announced that we
would be changing the default search provider to Yahoo!, and we
implemented that change for several milestones.
However, for the final release, we will use Google as the default
provider. I have asked the Ubuntu Desktop team to change the default
back to Google as soon as reasonably possible, but certainly by final
freeze on April 15th.
It was not our intention to "flap" between providers, but the underlying
circumstances can change unpredictably. In this case, choosing Google
will be familiar to everybody upgrading from 9.10 to 10.04 and the
change will only be visible to those who have been part of the
development cycle for 10.04.