I agree with your first sentence, but not the second one. I think the expectation was that IF the Sioux made the NCAA West Regional at the Ralph, they'd have a decent chance of getting to the Frozen Four. However, even when UND made the regional, many thought that having to play Michigan and then (it was assumed) Minnesota, the Sioux had one of the more difficult roads to Milwaukee.
While the 05-06 Sioux were a very talented and very young team, don't forget that the Sioux needed help from other WCHA teams to capture home ice for the playoffs and that on March 11, they were one game away from their season ending. Until Holy Cross beat Minnesota and UND beat Michigan, I don't recall expectations for UND being that high.