Consider the meaning of the word, "progressive". According to Merriam-Webster's website, www.merriam-webster.com, the definition of the word is
1 a: of, relating to, or characterized by progress b: making use of or interested in new ideas, findings, or opportunities c: of, relating to, or constituting an educational theory marked by emphasis on the individual child, informality of classroom procedure, and encouragement of self-expressionOf particular interest is the part of the definition that says "characterized by progress" as well as "making use of or interested in new ideas, findings, or opportunities". To me, this is at the crux of progressive rock. It's stretches the limits of the imagination, both in form and content. It seeks to advance the art, not simply capitalize on it commercially.
I don't know if most music critics would characterize albums like Snakes and Arrows as being progressive rock. I guess my music connoisseurship isn't quite at such a level. Few would argue that it's top caliber, but it seems to be much different from the seventies brand of progressive rock that included concept albums and atmospheric sound effects interlaced within the music. Of course, those are just two of the standout features that I remember.
I would say, however, that Rush remains progressive in spirit at the very least. Progressive in a personal sense, that is. When you look at the discography of Rush since 1974, the music has shown amazing diversity. Play Rush and then play Snakes and Arrows. You might still recognize Geddy Lee's voice, but it ain't the same music anymore. Pick any of the albums in-between and you will be hard-pressed to make any solid comparisons.
I think this is another amazing aspect of their music and yet another reason to induct them into the Rock and Roll Hall of Fame. With no disrespect to Rock Hall inductees like Blondie, who achieved the "amazing" success of three platinum albums (out of eight released) from 1976 to 2003, Rush has certainly outperformed most of them. According to Wikipedia,
As a group, Rush possesses 24 gold records and 14 platinum (3 multi-platinum) records, placing them fourth behind the Beatles, Rolling Stones and Kiss for the most gold and platinum albums by a band in music history.This was from the period between 1974 until today. Again, look at the music. Despite all of the changes in their music, they continue to make their mark in the music industry and haven't lost any fans yet. I would certainly call that progress.