IMHO, part of the joy of real piano ownership is the twice-annual visit from the tech. He takes real good care of it, well worth the money.
Once tuned, even the best pianos start to go out of tune; Just how badly/quickly depends on not jsut the piano, but how it's been tuned in the past, how frequently it's retuned, and environmental conditions. Swings in temperature and humidity will make matters worse.
I find that on my own piano, which I keep in a house that's generally stable temperature and humidity wise, still goes noticibly out of tune after a couple of months, and by the time the tech is on it again, it REALLY needs it. But then, I'm picky. Also, it seems that it's going longer now before it gets bad. It's still a young piano.