Hull normally get around 16k anyway although they'll sell out this I'm sure.
Derby had 2k more against Sheffield Wednesday than they did against hull yesterday.... I'd suspect the Derby fans are fed up with the playoffs also lol
For the big clubs like Derby, Hull and Albion this is all business as usual. For the smaller clubs like Sheffield Wednesday, it's a once in a generation thing and all manner of people come out of the woodwork for it, as was illustrated by the bumper crowd at Hillsborough the other night.