Rubens lost a place from start to finish at Silverstone yet Button did not (and they where only 5s apart at the end, compared to number of places thats very minimal). You seem to omit the part where Barrichello finished 2nd and Button finished 6th. Thats a pretty important point.
Germany - Button went from 3rd to fifth, Rubens went from 2nd to 6th
Yep. Button finished ahead of Barrichello. Fair enough.
Hungary - Jenson made up one place in the points - Rubens made up two places out of the points. Button outperformed Barrichello.
Valencia - as I mentioned before here Rubens clearly won - the only race where he does CLEARLY do better than JB. Yep. Enough said.
Spa - nothing can really be proved as Jenson only completed one lap - but coming 7th isnt that much to shout about from Ruben's point of view. We cant make any conclusions for this race.
Italy - they finished in the same position they started with minimal seconds between them (relative to each other). The fact remains that Barrichello outscored Button. Thats a fact.
Singapore - Jenson finished ahead after starting behind You forgot to mention that Button managed to get ahead of Barrichello, because Barrichello had a problem in the pits. Otherwise, odds are that Barrichello would've stayed ahead of Button. The fact is that Button finished 1 place ahead of Barrichello.
Japan - nose to tail ( and Jenson was faster thoughout the majority of the race). Once again, you forget to mention that across the full race weekend, Barrichello outperformed Button, culminating in Barrichello finishing ahead of Button.
So who was the slower driver again over all the races ?hhmmmmmm
I'm not sure about slower/faster, but the driver who was able to score more points was definitely Barrichello. Conversely, Button totally outgunned Barrichello in the first half of the season, when he had the car exactly to his liking.