Actually... the car analogy is a good one, because most of the wear on an internal combustion engine occurs within a few minutes of startup, when oil is not fully distributed and parts are undergoing thermal expansion. A car that has 50 thousand miles on the engine, mostly long-duration highway trips at constant RPM, will have much less internal wear than the same model, with 50 thousand miles of short trips to the corner store and back.
Something similar happens with electronic gear as well. If a scope has a combination of on-time and startup cycles that indicates it was turned on at 9 am and turned off at 5 pm every day for a year, that scope is probably less stressed than one with the same total time but 10x the number of start cycles, like it was turned on every half-hour during its year of usage. Every time you turn on a piece of electronic gear, it undergoes stresses both thermal and electrical that aren't experienced during constant running. This is especially true of vacuum-tube equipment, and also equipment with moving parts like hard disk drives.
Even Rigol specifies that their scopes should be on for at least half an hour before running the self-cal routine, and most anybody who uses scopes and other test equipment knows that allowing a half-hour warmup, even for digital equipment, is good practice before trying to make precise quantitative measurements. If I were buying used test equipment, I'd much rather have high time and low start cycles, than the other way around. Within reason of course.
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