If there's anything that's certain, it's the progress of compute power. The fact that his statement lasted 14 years is impressive. I mean, 640K ought to be enough for anyone.
That would be true if RSA keys were brute forced, but they aren't - e.g. 512 bit RSA takes days/weeks to break on commodity hardware these days, whereas 512 bit brute force (as is essentially needed for ECC these days) takes significantly longer than the estimated age of the universe.
You need to factor in speedups due to advances in factoring algorithms, too. And it's possible that the software doesn't have any options between 2048 and 4096. (I have no idea, I didn't check.)
Back in September, he issued a new public key of 4096 bits[1].
1. https://news.ycombinator.com/item?id=6376954