I think both Buick and Cadillac are very important to GM. Buick has topped JD Power reliability surveys for years, which GM really needs. While I am unhappy that GM is axing the Pontiac line, I can see why they did it. The line has been trimmed down severely. The G6 is a very average vehicle at best; the G8 while in my personal opinion is great car was launched about 3 years too late and is experiencing poor sales; and obviously the Solstice isn't selling enough to warrant keeping.
I would really like to see the G8 stay on in some capacity... but I doubt that will happen with the way things are today.
Good luck, GM!