Martin's writing is an unending abomination. I mean, the man can't even decide if he's going to use British English (arse, must needs, etc.) or American English (Dolorous Edd instead of Dolourous Edd, etc.). He has plot holes you could march armies of White Walkers through.

It's just entertainment. Like virtually everything mass-produced by Hollywood and better TV shows, if you think too much about it then it won't make a whole lot of sense. Martin isn't a thorough or very good writer. He, like Robert Jordan before him, has an entertaining story for what it's worth. However, like Jordan, he has serious pacing issues.

The TV series is better because it's tighter and keeps a much better pace. We know it's going to end because HBO won't keep viewers with a tedious series that goes nowhere. You might get away with that doing a modern-ish period piece like Mad Men, but in a dwarves and fairies and dragons fantasy show you'll drive your ratings into the ground. As for the books, the last two were virtually unreadable and just added tons of worthless plot elements (the fake Targaryan introduced at the 11th hour as though he was always there, for example). HBO pared away all that useless horseshit and kept only what was needed for telling a good story.

Fuck, I'll bet Martin had more than just a door planned for the books. Maybe he has some comfy sofas and a lava lamp in the cave with the Three Eyed Raven.