Just to point out something here - there's no such thing as stronger or weaker hw dithering - the 4x4 dither matrix is applied across the whole screen equally. Obviously, like with many other digital processing effects, they are only intended to work without blowing the pixels up

But to answer your question, 16bit buffers free up more fast memory. If 32bit doesn't look much different in the end result for a particular game, it's a worthwhile tradeoff.