Yeah, Minnesota doesn't have a great D, but Northwestern's D is much worse. They are far less athletic than what the Gophers have.
The stats don't really bear this out at all. Minnesota is worse basically across the board. They may have better athletes but they are also horrendously coached. Furthermore, JVB will have had two more weeks of practice with the 1st team under his belt when the Minnesota game rolls around, which should help a bit.