I believe it's the type of transformer, electric/mechanical (inductive) or electronic that operates the lamp and not the dimmer. Depending on the transformer type, the dimmer is selected. With X-10, again I believe, I'm not 100% sure, depending on the type of transformer you can either use a dimmer switch or just the on/off type switch.

If I'm mistaken on any of this I'm sure someone will point it out.