My only problem with Rush's merit as a prog band is that they were only prog at the altmost high point of their career... Their early efforts (mainly their first two albums) were not very prog at all, owing much more to Led Zeppelin, The Who and Black Sabbath than anyone else... They didn't really venture into prog teritory until Caress of Steel, and that was primarly only in the two long epics The Necromancer (no relation to the Van Der Graaf Generator song of the same name) and The Fountain of Lamneth.
Their first true prog album was 2112 and they were basically a prog band until the early 80s, when they adopted a more accessible radio-friendly, new wave tinged sound much like their peers Yes, Genesis and Jethro Tull did around that same time, in the 90s they returned to the more basic sound that they achieved with their early pre-prog era stuff, their last authentic prog record was Moving Pictures.