It's standard operating procedure in many palaces to drive a truck over a new mobile phone model then dunking it in a bucket of water before accepting them. There is no reason that tablet's can become at least that rugged.

Structural integrity declines exponentially. An 1/8th inch piece of glass the size of a credit card is pretty durable. That same piece of glass the size of a sheet of paper is rather delicate. On top of that, a phone screen provides a smaller target for falling debris.

So, even if touchscreen phones become popular on the jobsite, it will take significant additional engineering to get tablets there.