Actually, the Kindle is a tiny portion of Amazon's revenue, as well. And it's likely to stay that way for a long time, judging by the market resistance to e-books in general. Others have already mentioned that Amazon has a rather spotty history with e-books upthread. They're actually the company which is more likely to cut and run when the market doesn't mature in time. Amazon doesn't really care what it's selling, as long as it's moving boxes out the door. Their strength rests on two innovations: e-commerce techniques and inventory/warehousing logistics.
But it doesn't really matter. The e-book industry is barely large enough to be called an industry, and reader hardware is undergoing rapid changes as display technologies evolve. None of today's readers are likely to be around in five years.
Much of Sony's history with formats stems from the fact that they've always tried to use formats as a gravy train--create a format and then charge high licensing fees for its use. Competing formats have been licensed for a song or given away for free. Yes, the formats have lasted, but often the companies haven't. Phillips and JVC never capitalized on the formats themselves, and once their formats became commonplace, they were relegated to the status of "also-rans".
Beta's problem, by the way, was two-fold: licensing fees and expensive implementation. The format was just too good for consumer-grade equipment. The idea of a personal video recorder caught on better than anyone thought it would and the market demanded cheap gear. The commercial version, Betacam, is only now reaching its real end-of-life in the broadcast world.
Another thing to remember, while ragging on Sony for backing losing format horses. They're the folks that
went to bat in court to get home video time-shifting declared fair use in the US. Yes, it was self-serving, I'm not claiming otherwise, but that decision essentially created, or at least legitimized, the home video recording industry. Sony could have rolled over when Universal and Disney came after them.