gif owns png when it comes to animation. a statistic all of those sites failed to mention.
Probably because PNG isn't an animation format? MNG is however. I can't say how it compares to GIF because I've never used it. AFAIK it isn't supported in many programs -
yet. That will almost certainly change in the space of a year or so.
Why on Earth would higher CPU demand from PNGs be an issue in a few years (if that's even true)? It's not an issue now, in a few years processors will be even faster, why will it be an issue then? Bandwidth is a much scarcer resource than processing power.