Time for a Certs ad: You're both right, really. Bitt's Liebert links make certain aspects of this self-evident. It's not a matter or making things wet or dry, but of maintaining a humidity (the old relative thing) within an acceptable range. What you need to do, HVAC-wise, to stay in that range is quite different between winters (generally drier) and summers (generally more humid) and between Richmond, Virginia (humid) and Tuscon, Arizona (dry), so systems are designed to compensate in both directions. Cooling a volume of air reduces the amount of moisture it can carry, so you may have to compensate for that, likewise if you warm the air (or don't cool it as much) the opposite applies. If it all works well, the end result is "pretty dry" (TM)

Static is and isn't a big deal. Even with grounded floor tiles and racks you can still generate a nasty spark to ground. Not every shop requires (or wants to wear) ESD booties for routine walking around, so reducing chances for static build-up (say, by keeping humidity within the target range) is considered a good thing -- also good risk management for the tech who didn't sleep too well and who forgets to put on his ESD strap before doing a board swap.