I'm not saying that you don't have a problem, but I've had the same issue with Lutron dimmers. This is copy of the response Lutron's technical service sent me when I questioned the same problem.
>>>>>Thanks for your e-mail to Lutron. The dimmer can safely reach a temperature of 150°f above ambient room temperature. If the heat is bothersom to the customer they can purchase nylon screws to help stop the transfer of heat from the dimmer to the face plate. <<<<<
I've tried the nylon plate screws and they seem to do the trick.
