GNLaFrance . . .
You are correct about bullet diameters being different, but so are the bores of rifles . . . even within the same make and model.
Most carton .22LR range from just under .223 to slightly larger than .224. In general, I've found autoloaders to like the larger diameters. Bolts, Levers, and Pumps seem to like the smaller diameters. Of course, this is a generality and I myself have rifles/pistols that don't follow this recipe.
The same can be said of .22 WMR, but this is where you're hypothesis holds true. Most .22 WMR use a harder alloy than .22LR for bullets. They also seem to be more consistant, not quite .224 but not less than .223 . . . mostly. The softer bullet of .22LR alows them to expand into the rifling of various diameter barrels, so they can have a little play in diameter.
This is one reason why different rifles like different .22LR/.22WMR ammo . . . bullet diameter. My CZs like .223, my Browning autos like .224.