This is a good example of it done extremely well, also from Apple.

http://www.apple.com/imac-with-retina/

It's even more impressive when you inspect it and see how it's done.

How is it done? I see a couple of css transitions but there must be some js involved as well?

It's a large div with a ton of canvases inside, the scroll wheel is also linked to a css transition on the div the scales it outwards.

Yes. They linked the scale of the image (CSS) to the scroll wheel with a bit of JavaScript.

Hell yeah, thanks for sharing!