Google just dropped Trillian from the Google Pack, without any notice to Cerulean.
Scott Werndorfer, co-founder at Cerulean :
Our goals are seemingly no longer perfectly aligned with those of Google. Their reasons for removing Trillian are their own and were not made available to us.
Google spokeswoman, confirmed the removal :
Google Pack is currently in beta, and the selection of software available through the Pack will continue to evolve
My best guess, is that they initially added Trillian, just to complement Google Talk, as worldwide IM usage goes, versus the immediate rival Yahoo Messenger.