I agree though not sure its entirely an innovation problem. I have an M8. A few friends have one too. It does what I want it too. I am not sure what the M9 could have done to be an upgrade. Certainly there isn't a competing offering inspiring an upgrade either.
A lot of people I know upgraded last year and all are waiting til at least next year for their next upgrade (barring loss, or damage). All the HTC owners are planning to stick with HTC when the upgrade comes around.
Apple meanwhile are flying just on the back of making the phone bigger and their ecosystem lock in and brand loyalty. (I did manage to extract my girlfriend from the Apple Lockin a few weeks ago by getting her a second hand M8 off eBay for £200 - shes never been happier).
Samsung have made a leap in construction quality which is probably driving their loyal customers upgrades.
I guess I think the M8 was just so good there's nothing to drive upgrades and the other manufacturers have caught up. Be interesting to see what the landscape looks like next spring when its upgrade time. If someone comes out with a platform I can EASILY dock and use as an office PC then that might tempt me. I can't think of another killer innovation I would switch manufacturer for.