>>225
Well, as for the "JPEG is best for game screenshots" comment, that really depends on the game. If you're talking about a 2D game chances are very high that PNG is going to provide the superior file size in addition to being lossless. It's a matter of how objects are colored and animated that gives PNG the edge. If it's a 3D game though then yes JPEG will usually get the point of the image across the same while saving a lot of space. In a 3D game the colors of something from frame to frame can differ much more radically due primarily to lighting systems.
It is actually possible to do lossy PNG however, so JPEG may not be better in as many situations as one might think.
http://pngmini.com/lossypng.html
How all this relates to animated PNGs is that you're going to have a big file if you try to animate something with a lot of colors and little consistency between frames. A genuine video format like WebM, MP4, AVI, etc. is basically the animation equivalent of JPEG.