I think that had a lot to do with Dow Corning bringing tough conductive glass to market. I have an old kitchen scale which looks remarkably like an iPad to a casual glance; it's got a black glass top, and measures the weight function via very small recessed feet it sits on. You switch it on and recalibrate for tare by just touching the appropriate icons in the corners (which actually work by optoelectric sensors rather than via conduction or pressure). It's like this one: http://www.amazon.com/Salter-1041BKDR-Glass-Electronic-Kitch...

The glass cover thing has been in kitchen and bathroom scales for a while, since they're likely to be exposed to fluid/powder on a regular basis.