This might have made sense a couple of years ago, but I don't think desktop hardware is advancing at a rate where yearly updates are a must. This seems even more true for typical Mac use-cases where users don't quite care as much about gaming performance. Intel deprecated tick-tock for a reason, so I don't think it would make sense for Apple to adopt that strategy now.
I don't think it needs to be a rigid update every year but they should have a policy of not staying more than one generation behind. The 5K iMac jumped to Skylake, so that's fine, but the rest of the iMac line is stuck on Broadwell, the Mac Mini is Haswell, and the Mac Pro is Ivy Bridge.
The solid industrial design, long service life, etc. are worth something but probably not 3-4 hardware generations, especially for the premium market Apple wants to be in. The PC market hasn't been completely stagnant and while nobody is buying a Mac for super hard-core gaming they really don't want to be in a position where someone drops a fair amount of cash and their new computer struggles with a game which came out a year or two back, 4K video playback, etc.
http://buyersguide.macrumors.com/#Mac shows the days between releases in the past:
We're currently 380 days since the last release, which is on the long side other than the one 2010-2011 outlier. I don't think anyone expects Apple to ship radically different hardware designs every year but they desperately need a tick-tock strategy which ships identical cases with non-obsolete components if they expect anyone outside of the die-hard Mac fans to keep buying.