Why No Power Button on Some Phono Stages?

Lewm -
Memory distortion in audio components, ie resistors and capacitors, is recognised by many now. A common example that some people may be aware of is batteries. If you keep recharging a battery before it is discharged fully, it can form a "memory" whereupon it wont work any more when it reaches that point that you kept recharging it, whereas if you completely run the battery down before recharging, then it will work at all levels.
I run tube preamps where the operating voltages are quite conservative and therefore can be left on all the time.
What I am saying is that if I dont discharge the power supply completely from time to time then those power supply electrolytics will form a memory ( similar to the battery example ) as they have never been fully discharged, or even overcharged on turn on.
Another way of thinking about this cycling, is degaussing your cartridge.
And the answer is yes, I hear a freshening up of the sound when I turn off the components for a day or so.

Dover, How do you discharge PS caps? Turning off for day or 2 may not do the trick and still keep'em charged. It's highly recommended regardless of unit being turned on or off to discharge caps with 1mOhm resistor before any 'surgery' on electronic equipment for certain reason and if you want to verify it, you can (certainly with your own health risk) touch terminals of your power supply caps just to verify and test the information you currently believe into.
As to sound differences, you're simply listening to the 'colder' rig than one was running for a month 24/7. Speaking of electronic components, normal operating temperature is very important to have specified parameters, but excess of temperature can also be even more destructive. In solid state electronics the vibrations against heat sinks will cause loss of integrity and certainly higher running temperatures. In tube electronics in general LOTS of components exposed to the hot running temperatures. It also tells that turning off even solid state devices, will prolong length of good performance.

If you keep recharging a battery before it is discharged fully, it can form a "memory" whereupon it wont work any more when it reaches that point that you kept recharging it, whereas if you completely run the battery down before recharging, then it will work at all levels.

Can you specify what kind of battery has such phenomenal capabilities?

Straight from the horse's mouth:
https://rolls.com/doc/manuals/manual_VP130.pdf

Always turn the unit off when you are not using it. This will help keep your VP130 sounding like new for a longer time, and saves electricity. We recommend connecting your setup to a outlet strip so you can turn on all your phonograph equipment at once.

Spike, The VP130 is a simple tube phono stage. Most tube units in fact ought to be powered down when not in use. I don’t think there is any argument on that. For some tube units with solid state rectification, it is possible to leave the power supply in "Stand By" mode when not in use. In StandBy, the SS rectifiers and PS capacitors may remain charged up due to voltage drop across them but with no current or voltage flowing through the active circuit. The Bellari apparently has no such separated power supply. Most solid state units probably benefit from being left on all the time, and those don’t need a front panel on/off switch. Though it’s nice if they have a rocker switch in the rear, next to the IEC power cord receptacle.