Microcontrollers - are the output states constant or multiplexed?
The way I interpret the question has nothing to do with PWM, sorry if I am way off base, but it sounds like you used it as just an example.  

Pretty much every type of microcontroller and devices with I/O use a latch/FF to drive their output circuitry.  What this means is, when you set a state, it stays in that state.  It is not like DRAM where the output stats have to be constantly "refreshed" in order to stay at their state.

With your glass example, I have never seen any hardware that would pick up and put down the glass on the table repeatedly.  It would only ever put the glass on the table, and leave it there until a state change is requested.

Going back to PWM (just in case you were actually asking about PWM).  Whether you bitbang it or your microcontroller has dedicated hardware as other posts outlined, the I/O block is only accessed and modified if a state change is requested by running code or the PWM peripheral.