Do really "all mechanical watches need to be maintained properly"?

Somebody answered this on a different question:

All mechanical watches need to be maintained properly. Every year or two they should be taken to a watchmaker for a service. This will include lubricating the watch, checking the bearings, for signs of wear and checking the seals within the watch to ensure their specified level of water tightness.

Other than being fascinated with old-timey watches and their mechanical beauty, I actually bought my mechanical pocket watch (quite recently) for the purpose of not having to go to some store regularly to have the batteries changed. I know there are "kits" you can buy to do it yourself, but after watching instructions on how to perform that, I got convinced that I didn’t want to risk damaging my watch by "doing surgery" on it like that, not to mention it’s yet another thing that eats batteries and the sheer stress of knowing that it has to be done at some point. I much prefer the idea of mechanically winding up the watch daily or when it’s needed instead.

But now, according to this person, even my mechanical pocket watch has to be "maintained" with me being required to go to some store/watchmaker (not even sure if these exist at all where I live anymore…), even though it has no battery or electronics. I expected this thing to be going forever as long as I wind it up, possibly breaking after many, many years of constant and heavy use.

If I were to follow the maintenance recommendations for things, I would do nothing other than maintain my stuff all day. Is this really necessary? What would cause such a "closed" system of physical objects to require somebody inspecting and fiddling about with it?