@kasya_carey: I agree that they are equal and Magneto has shown more versatility (since most writers prefer to use storm as lighting lass). I think the nature of the person also matters.
Like Jean can snap necks, explode brains or rip eyes out. But doesn't because of the type of person she is. The same for Storm, she doesn't start her battles by splitting hydrogen atoms or frying synapses or fish freezing or removing the ozone layer to burn the area.
Unlike magneto who would start by ripping people apart or manipulating iron in their blood. I believe if she tried, she'd be able to do the things he's done.
@marvelfan1992: wasn't there a time in Bunns run where Magneto went to Xorn to heal his powers. It's all over the place.