An authentic plastic wheel has a steel washer inside. I think that washer would make it strong enough even for the heaviest lightsaber props, so there would be no reason to make their own unless they couldn't source enough of them — but they were quite common back in the '00s, so I don't think that's the case.
Some replicas have wheels of anodised aluminium simply because those looks nicer up-close. Wheels dished on the bottom to the curvature of a cylinder were also invented by fans.
I scrutinised my image collection: Anakin AOTC, Dooku, Sidious at SW Celebration 3 and a "Shaak Ti Episode 3" saber in an exhibit all have wheels that are satin black with the moulding line across, like authentic plastic wheels do. I don't have up-close images of other sabers from Episodes 2 and 3.
Edit: I do have a plastic wheel with no washer in my parts drawer, but it is missing the parting line and the slit is narrower. I have no idea where it comes from. (Master Replicas?)