I say it's more technique. Way less that the rim actually has anything to do with how easy they go on.

Though if you are putting any tire on a skinny rim with a tube that's taking up the space the tire bead should be in while being installed, then yes the rim might be an issue over a wider rim with a deeper spoke channel. But still, with good technique and practice even the worst of rims are easy enough to overcome without using levers.