Meh. He's had plenty of time to write and when we're talking YEARS between books the whole "factory writing" thing doesn't exactly take.
You can say that, but my perfect example of this would be Stephen King's Dark Tower series. He wrote the first 4 books over a 15 year period and they were all excellent. He then had a brush with death and churned out the last three books over 3 years, and they were all mostly garbage.
Sometimes an author needs a break to write something else to keep him from getting stagnant on his main series. I've been reading this series since 1996 when it came out, so I'm as pissed about the delays as anyone, but I'd rather he take his time and put out a good product rather than rush out some garbage.
That being said, Martin does seem to take slacking to extremes. Though he is self admittedly terrible at deadlines.