The difference between Eastern Europe and Cuba is Communism was imposed by Soviet tanks there and was perceived as the instrument of a foreign power. In Cuba, it arose through a home-grown revolution and is seen as a nationalist bulwark against American designs on the island. For that reason, Communism is going to have a longer stay in Cuba. The country might become more like China or Vietnam but the ruling class has no reason to cede power.
(No more Olmert! No more Kadima! No more Oslo!)
Yes, and I would add one other point. Cubans, or most of the ones who remain there, are third-worlders. In Eastern and Central Europe, communism contrasted starkly with an older and better civilization. It is no accident, I think, that while Eastern and Central Europe threw off communism, no non-European country truly has, even though it's clearly decayed in China and Vietnam.