Well, sort of. It is not so much about reducing weight or size; the rover weighs 900kg (basically, one US ton). It is about energy budget; with the radioisotope

Well, sort of. It is not so much about reducing weight or size; the rover weighs 900kg (basically, one US ton). It is about energy budget; with the radioisotope thermoelectric generator, "nuclear battery," there is ample power not only to move such a behemoth around, but also to power some really interesting scientific instruments. For example, the rover has a laser which can vapourize a small sample which can then be analyzed spectrally to get chemical composition. Imagine trying to power a laser like that on solar panels.