I agree with lostarchitect. At least with a Sturmey Archer AW (3-speed) hub, it's very easy. Disconnect the shift cable, unbolt the wheel. It's out. When reassembling, reconnect the shift cable and adjust the gears. I can literally do this with my eyes closed. Seriously.

IGH truly does take less maintenance. Snow and salt and road grit are hardly concerns. Chains are wider and intrinsically stronger. The fact that you don't shift also contributes to their life, and chainguards that keep them clean help also. A self-closing door can bend a derailleur hanger. It happens a lot, and then the resulting failures from shifting the derailleur into the spokes can be pretty bad.

But having said all that, I still use derailleurs. IGH can be a very good choice for many people. It's more costly, and it weighs more.

Repairs on a 3-speed hub are simple and cheap, and they are rarely needed at all.

Repairs on 7- and more-speed hubs are expensive or difficult. I believe 5-speed is somewhere in the middle. So some of the great attributes -- long term reliability and durability -- given to IGH really apply mostly to 3-speed hubs.

And as some have pointed out, 3-speed hubs have, duh, only three speeds. That's fine if you don't mind slowing way down when you downshift, but some of us like to sustain a certain amount of effort throughout all terrain.

I do have one three-speed bike, a 1962 Rudge Sports. It came with a 48T chainring and an 18T sprocket. I replaced the 18T with a 24T, so now all of my gears are low. I can tow a heavily-laden trailer with it and climb hills doing so. When I go fast down a hill, my top gear is too low to pedal, so I coast, which is fine with me.