the closest thing I have to hard numbers were these estimations from the Kickstarter video. I checked the vram of the exported pngs using frame by frame animations to that of the Spriter based animation, and multiplied to get the higher frame numbers:
I didn't use a benchmarking beyond simple vram queries, and it's probably a little more complicated to get an accurate number than just multiplying, but the basic idea stands.
The best way I can explain it is visually. Here's a spritesheet: (<img src="https://dl.dropbox.com/u/1013446/Spriter%20Releases/qrbcjcoc2.bmp" border="0">
(original link: http://www.fabiobiondi.com/blog/2012/08/createjs-zoe-create-spritesheets-in-adobe-flash-for-easeljs/)
look at the spritesheet as the cost of vram. In Spriter, you could recreate the same animation from roughly this amount of vram:
<img src="https://dl.dropbox.com/u/1013446/Spriter%20Releases/qrbcjcoc.bmp" border="0">
With traditional sprite sheets, if you wanted to make the animation twice as smooth, you would have to double the size of the spritesheet, which would take up roughly twice as much vram. With Spriter, it can tween as many frames as the engine can handle in realtime(usually over 60 on any recent device) while still using the same amount of vram.
You could of course add variations of body parts for different facial expressions or turning the head, and make a much more complex character, animating at 60 frames per second, and still use less vram.
It comes at the cost of a little cpu power, and some ram to hold the animation info, but vram is usually in very short supply in 2d games, while cpu power and system ram aren't. This is why games animated with modular animation like Odin Sphere and An Elysian Tail can have such large and smoothly animated characters.