I'd say that if you're lucky enough to not have joint (or other) issues, stairs won't be a problem even if your home is single story. If you have mobility issues, then stairs will be a challenge, even if you have plenty of them to 'practice' on!
NannaPat
That's the most sensible remark I've read on this thread.
kircubbin I can sympathise - we never know when mobility issues may suddenly come upon us or if we might injure ourselves, making stairs difficult to negotiate.
We do have stairs but I'm thankful for our downstairs loo.
Yes, I've heard of "bungalow legs" but it's not always a case of use it or lose it.
I recall when a Physiotherapist gave a talk to a ladies evening. “Ladies”, she said, “don’t move to a bungalow unless you really, really have to - keep your stairs ”.
And when you suddenly have to then it's not always easy to find somewhere suitable or even have the energy to deal with a move and all it entails.