It's the standard for high-content images (photos, etc.). GIFs serve an entirely different purpose (low-content-- logos, etc.).
For the Web. But in pro and print work stuff is different. Microsoft is also aiming at the pro crowd, and luckily they don't have a monopoly there. Their attempt at a PDF competitor is not doing well, because they forget it's not just about some software, it's about a huge publishing workflow where both hardware and software is geared to PDF and PS.
Aside from an OS used by some, Bill Gates doesn't have much of a presence in that industry, except for Corbis. Expect Corbis stock images to start being available in this format as an option, and later as the only option.