NEX-VG20 - why no sensor overheating ?

Thanks, I have the NEX7 (with 18-55 Kit) and just bought the VG20. I bought the VG20 primarily for worry-free video, where one does not have to be looking out for sensor overheating and the 30-minute limitation per clip. Of course since it can shoot stills (including RAW), that is just icing on the cake.

Still debating whether I should keep the NEX7 or just return it and keep just the VG20, since I already have the A900 for top-notch stills.