Martin actually addressed those two things on his website, basically saying to his fans that this series is not the only thing he does. In fact, he's more into his sci-fi, it just happens this series became the most popular. He also poked fun at people who say he's fat and old and is going to die before he finishes. I myself have had that concern, lol. I surely hope he gets to finish it.
A Feast for Crows and a Dance with Dragons is basically one big book, it just turned out to be too big for only one, that's why each one is basically half the characters only. The last two books will be the traditional all characters stuff we're used to, at least assuming they don't run too long on him as well. =)