Those are really nice, and the gallery goes a long way toward making the case for it.
It's worth underlining the fact that "lossy" here means "really nicely dithered 256-RGBA-palette PNG8s", but (as the gallery examples demonstrate), that may be sufficient for most of the kinds of images that have significant transparency and that would be likely to be found on a webpage (even sprites for a canvas game).
Honestly, I would still like to see WebP support in spite of its drawbacks (thanks software patents!) for it's better definition of "lossy" and for saner alpha compression, but between better pngs from software like this and upcoming support for DXT5 in WebGL, most of the compelling market drivers may be gone.
There's also a second option — adaptive posterization — that reduces PNGs by ~30%. Useful for images that are too "colorful" for 256-color RGBA.
WebP is a fine format, but establishing a new format on the web is really hard. There's a graveyard of better JPEGs, and after 16 years since PNG was published, GIF is still alive and well. http://ycombinator.com/images/y18.gif
The web has strong preference for "good enough that works everywhere". IE6 was enough to discourage devs from using PNG, nad you won't see Google's WebP in IE or iOS anytime soon.
Nowdays you can decode WebP with JS, but size of a JS decoder and CPU time to run it will most often offset any savings from the format.
It's worth underlining the fact that "lossy" here means "really nicely dithered 256-RGBA-palette PNG8s", but (as the gallery examples demonstrate), that may be sufficient for most of the kinds of images that have significant transparency and that would be likely to be found on a webpage (even sprites for a canvas game).
Honestly, I would still like to see WebP support in spite of its drawbacks (thanks software patents!) for it's better definition of "lossy" and for saner alpha compression, but between better pngs from software like this and upcoming support for DXT5 in WebGL, most of the compelling market drivers may be gone.