I'm not sure what point that website is trying to get across, they're comparing measured wheel power with manufacturer's quoted flywheel power, which will only confuse people who don't understand transmission losses
Especially when 4wd comes into the equation.
Indeed and its made even more complicated by the fact its a hub dyno
You can have @ the wheels from a normal brake dyno (includes losses to tyres , variations from slippage etc)
but in this case its @ the wheels (i.e. hubs) so the tyre losses/problems are removed , so the wheel figure should be greater.
Check out
http://www.pumaracing.co.uk/ and the technical articles.
Although remember for a hub dyno (no wheels) the calculations no longer hold!
S3 vs S4 , are they the same diff setup? , do they shift power differently? , was it measured at 4 hubs or 2 etc...
[In fact looking at site I can see it measured via all 4 wheels.]
[And the S3 looks to have only been run in 2wd mode , no rear pickup in picture I can see.]