but there ARE ballasts out there that take 480v...two 'hots'...for their input voltage.
Very true, we install hundreds of them in parking lots, heck we would use 600 volt if that was available.
The high voltage keeps the costs of the raceways and conductors under control.
However as mxslick mentioned the input voltage is not the voltage at the socket.
Most newer ballasts have the socket voltage marked on them and it is a range.
It will say "OC voltage xxx"
For example a 400 MH ballast if I remember correctly has a open circuit voltage around 280 volts.
But to answer the opening question in general no you may not interchange lamps without changing the ballast.
There are a few lamps that interchange but look at the ballast and it will tell you what are the approved lamps.
I always order HID lamps and ballasts by the ANSI number.