yup, they are not just magnesium, as they would cost a lot more.
They just have a higher magnesium content. Generally magnesium wheels would shatter rather than bend. Watching Rallying will show that.
At the end of the day, if your hitting a wheel hard enough to 'bend' it, no matter what its made from, its gonna get fooked!!
I unfortunately didnt weigh a standard wheel before i sold them on, so have no weight comparison.