humidifier? really?

OK, so it's been stated pretty uncontroversially both here and at Everything Dulcimer, that a wood instrument is susceptible to excessive dryness and if you live in an arid climate, you should make or get a humidifier for your dulcimer. Since I live in a place where it doesn't rain from March until November and where we run the heater most of the time during the rainy season,I took that advice and bought a couple of those guitar humidifiers (the little clay things in the plastic containers) and put them in my guitar cases. I now have a couple of dulcimers with some monetary value and am about to do the same, at least with the one that has a hardshell case.

But this is my question: really? Is this really an issue?

My daughter's piano teacher and her husband are bothprofessional cellists. Theyown cellos that are worth morethan my car. Neither of them have ever consideredusing ahumidifier.

Is there a reason why a $500 dulcimer would need a humidifier but a $15,000 cello wouldn't?