[ronaldj]

Yes yes yes we do! Bandwidth may be increasing, but as displays get better we are going to be serving up ever increasing assets. Sites are already serving up 2x'd versions of images for iOS devices that have higher resolution screens. These higher res images essentially quadruple your file size. On top of that these devices are mobile, which lag behind broadband/ethernet connections AND many of which have data limit caps.

[pornel]

Sizes of "Retina" PNGs can be halved just by using better PNG compressors, here's real-world example:

http://imageoptim.com/tweetbot.html

It's annoying that we have the tools. We don't need new format for this, just use what we have already!

[ronaldj]

But you won't get the file size of a lossy WebP image with an alpha channel.