Actually you need to look into the feature list if you think the HD2600 has the same support as the HD4650, and same with the GF9600GSO, since they all support different feature leves. Whether or not he will use all those features is another story.
Besides, Nvidia has its own PureVideo playback, in competition with ATI's AVIVO. It's not like 9600gso don't offer video acceleration.
It does, but you need to look further into the differences, because you seem to think they are all the same, and they are not.
The HD2600 reference is in reply yo your CPU comment, because if it were to be playback feature wise, the GF9600GSO definitely has a slight edge over the HD2600, however in addition the HD4650 also has additional features ontop of that, which is the point of the recommendations. Whether or not he'll use all the features or not is another question. However for the tasks he's listed, there's nothing the GF9600GSO would be a 'better performer' at than the HD4650, other than the gaming which he already mentioned is not the focus.
So what exactly is it that the GF9600GSO does that makes it your recommendation? What is this 'performance' difference you allude to.
What to shed some light on it, because right now it looks like you're confusing gaming performance and adding it into a thread/choice where it's not relevant.