It's what the experienced basketball watcher/fan/player sees. We see it, it's not hard to believe it. The rest of the B1G outside of UW fans agrees with this sentiment. The only other biases that seem to come close are the pro-OSU and especially pro-Indiana ref biases.
You made a decent point with the stats. I hadn't seen that before so it makes me think twice, but I'm sure my eyes don't deceive me. Like another poster said, it's the TIMING of the calls. Like say the Gophers have a 10-point lead in the second half at Kohl Center, suddenly it's ticky-tack this, ticky-tack that, send UW's best FT shooter to the line if someone breathes on him for the better part of an important 5-to-10 minute stretch, while Wisconsin is allowed to murder the opponent. The entire momentum changes on the extremely biased, if perhaps temporary, reffing, and UW gets out of the tank.
That UW has such an amazing home record compared to their record as a whole over many of the past years is the proxy data that you are avoiding. No way UW has such an amazing home record based solely on deserved merit - they are getting a ton of assistance by the referees (and on the road in the B1G, for that matter as well). The refs let UW own them, whatever entity is behind it. The same calls are simply not called on both ends of the court when UW plays a B1G game, home or away. It's obvious.