You make a very good point and few glass workers ever consider this. Any of these activities that generate a mist around the machine include these tiny bits of glass in the mist. Flat laps, in my experience, generate less mist and spray if they're set up right but they still produce shards in mist. I use all of the above tools at one time or another and I always use a mask, even when working outdoors with my bigger saw.
It occurred to me one day a while back that mist is the equivalent of sawdust from the woodworking world (I'm a reformed wood turner) and dust control is important for maintaining your health in that business.
If you do a lot of cold working and don't use respiratory protection then, IMHO, you're opening the door to respiratory problems and possibly silicosis.
My favorite device is the Triton respirator system that I bought for the wood shop (
http://www.tritontools.com/). You get impact, noise and particulate protection in one package. It's not cheap or particularly stylish but it's very good for a number of different applications, up to and including running a chainsaw.
Robert