Re: Pure video = VDPAU ?
VDPAU only supports graphic cards that decode the entire video stream on dedicated hardware. This is Geforce 8 and up. Earlier cards only did partial decoding on dedicated hardware, the rest was done with shaders and/or in software. These shaders would very likely need to be rewritten for Linux, something Nvidia it seems doesn't intend to do.
Any documentation mentioning PureVideo (or PureVideo HD) is not valid for VDPAU. The names are different for a reason - they're not the same thing. At all.