I have a 14" B&W Admiral set with instant-on. My grandparents have owned it since new. I think it probably spent years at a time plugged in, but I always unplug it after use 'cause I don't like this feature either.
As far as I know, this set has never been serviced. Still works excellent.
My B&W Zenith keeps a couple tubes on in the Space Command Chassis (I unplug it too!)