The only reason I asked this question is because I have a hard tonneu cover on my pickup and didn't feel like removing it to bring the water heater home.
However, it would be completely foolish/lazy of me to risk damage when I do have the means to transport it without laying it down.
I also didn't want to lay it down right in front of the salesperson, damage the dip tube, gas valve or anode rod and then potentially have to exercise a warranty at a later date. Commonly known as "pound wise and penny foolish".
As far as the refridgerator, I heard that if for whatever reason you do lay them down, you also stand the risk of the compressor falling off the vibration absorbtion cushions inside the casing. I also heard that if you do lay them down, you have to let them stand upright for awhile before plugging them in.
I'll have to verify this with the part-time, high school kids at Lowe's.