Where do you get that from?
My own experience. Please note that I am comparing helicopters with medium and heavy fixed-wing aircraft with pressurized cabin. Also, the smaller helicopter the better. If it's due to the fact that smaller helicopters normally have less good performance I don't know. I just know that I don't feel the pressure difference in an R22 as I do on a medium or heavy fixed-wing. Also, some fixed-wing aircrafts are better than others. I rather fly a B737 than an MD80.
They can still climb and descend can't they?
Can they?