Operational Junction Temperature with LM7800 series regulators
It seems like a 50°C increase for just 1W thermal dissipation is a lot


This is accurate for many TO-220's, a TO-3 would only rise 35°C for 1W of thermal dissipation because it has a much larger body that acts like more of a heatsink.  Simply add a heatsink to keep regulator 'cool'.  

More help on this is addressed well here.