Well, it seems altogether possible that the sticky gray material that you notice on the TV remote and the garage remote control is generated from your hands. Just to give you an idea of how these are carriers of illness, a recent study found that TV remote control leading carrier of bacteria in patient's hospital room --- even more than the toilet bowl handle.

You can always take these controls to a diagnostic lab for a swab and analysis if you really want to know what the material is. However, I suggest that you simply clean them once a week. Even a wet paper towel will do it...but a gentle cleanser like CitraSolve (made from real orange oil) can also eliminate germs and bacteria.