Also, looking at the Pollster.com database this information was taken from, polls used to create this info for 2008 House races are 45.1% partisan/internal polls, while 2008 Gubernatorial race polls are only 28.8% partisan/internal.
In addition, while I was only counting through to determine the above, I did notice that the House elections had a much higher occurrence of random uni pollsters and such compared to the Gubernatorial elections.
I didn't look through the Senate election polls but I'd imagine they'd be very similar in composition to the list of Gubernatorial polls.
I think the reduced accuracy of House polls found in your link, cynic, can be mostly explained by pollster quality.
I know that single-member district polls throughout the world always have some accuracy problems, which is to be expected when polling a district of, say, around 100,000 people. I think this error would be much more reduced in US House elections, however, compared to elsewhere, with the average Congressional district population being greater than the four least populous states- and I don't think polls in AK, ND, VT, or WY are any less accurate than NY or CA or what-have-you.
