I don't think GRRM's case is any way comparable to Tolkien's. Tolkien lived in a different age, before the availability modern technology such as word processors.
Not a very convincing argument. CS Lewis wrote his NARNIA books with the exact same lack of technology as Tolkien and churned out all seven of them in less than half the time LotR gestated. Not to mention many, many other writers also bashed out lots of words in a short period of time long before the advent of the word processor. Although 'word processor' may be a generous description for the 25-year-old programme GRRM uses to write his fiction
A world wide war loomed and was fought, he had duties as an Oxford University professor, he was working on other books such as the Silmarrilion, and had not bound himself with specific promises to fans. And Tolkien finished the whole story before he published.
The bulk of LotR was written in 1939-45, when Oxford University's normal curriculum was suspended as almost all of its would-be male students went to war instead and Tolkien actually had a lot more free time than he had prior to it, especially since he was not chosen to help with war office work. Tolkien also made specific, repeated promises to his publishers on when the book would be completed. He sent letters to them promising the book's completion in 1941, 1943, 1945 and more that he repeatedly failed to meet. Worse, we now know he on several occasions wrote letters to his publishers promising he'd make progress or 'big pushes' on the book during periods when he'd written nothing. This wasn't due to lack of ability or writing speed when needed - Tolkien wrote the entirety of Book IV of LotR in about three months - but purely down to procrastination and writing blocks.
Martin, on the other hand, has been quite upfront at reporting when he is not working on the book due to other commitments (mostly overseas travels). I grant that GRRM could have been feeding us Tolkien-esque excuses and even flat-out lies to cover a lack of work, but from mutual contacts and friends this does not appear to be the case.
The gaps between Martin's books was two years for the the first three books, five for the fourth and at least five for the fifth.
Again, that is only the publication time. The writing time is a different story altogether. With the exception of ASoS, none of the books in the series have taken less than three years to write, and one other (AGoT, although incorporating part of ACoK) has taken about five. Whilst now approaching outlier status, ADWD's writing time is not outrageously long in comparison.
Rowling managed seven Harry Potter books in ten years for example!
Again, only going by publication date. Rowling began writing the series in 1990, however, so that's seventeen years for seven books totalling about 3500 pages, contrasted with
ASoIaF's eighteen for four books and three novellas totalling about 3750 pages.
Fancy that, GRRM is just as slow a writer as JK Rowling
But it's not just that. Someone did an analysis of George's blogging somewhere (I don't recall where) and reported that George had written something like 70,000 words on his internet website since AFFC, but only a very small proportion of his blogs in the summer of 2009 concerned the fifth book. Mainly he was interested in other things, such as the TV serial of book one and on pushing some of his other works, and in his social interests such as football (as you point out).
This despite the previous broken promises regarding when ADWD will be ready.
GRRM did not comment much on the writing of ACoK or ASoS whilst he was writing them either, and had previously stated on several occasions he would not be offering blow-by-blow updates on the writing of ADWD or any other book for concerns of spoilers.
On the last point, he ceased giving any possible dates for ADWD
because of the previously incorrect estimates regarding when ADWD will be finished (starting with the one in the back of AFFC).
Another thing that worries me, and this is of course purely subjective, is that AFFC, having been published after a 5 year gap, was noticeably inferior to the first three books imho.
This could be the start of a trend, and I agree the dip in quality with AFFC (although not unexpected given the reports of the book's difficult nature) did raise concerns to those of us who had been through this before with Robert Jordan. However, it is purely fear, uncertainty and doubt at the moment that makes people fear the same will be true of ADWD. This is one criticism that cannot be answered until the book comes out, although the fact that it is nearly done and GRRM has reiterated that the series can be finished in two more books is a hopeful sign that there will be no further splits, divisions by POV character or so forth.