No one has mentioned tire differences causing a reduction in dyno results here. Tires with additional siping in them cost power as well. Back when I had my Evo it dropped 15hp switching from Pilot Sports to Conti All Seasons. No changes in equipment, and same day dyno results. I swapped them just for fun, same wheel fitments.
Often times guys and girls swap wheels but also run different tires, which will vary the results as well.