My understanding is that the problem is only with square dies in the largest sizes. The 5-inch square die is the popular one that has this problem on both the Go! and the studio. Personally, I think it has to do with the fabric stretching under the roller. The smaller dies are rolled through at an angle, but the 5-inch die is too big to be rolled through at an angle -- at least on the Go!. My bet is it can't be angled enough on the studio.
I bought a Go! for my sister that we haven't had a chance to use yet. I'm just not going to buy the 5-inch die; we can rotary cut 5-inch squares. All of the other dies appear to be very accurate.