Not quite...
Here's why I think so.
A person needs water, food, and -- depending on the environment -- shelter. For the 1 million people displaced by Katrina, it was the lack of some or all of those that lead to displacement to a location that had all three. But if you lack any one of these, you are just as surely in a condition of displacement since, if you don't get to a place that has all three, you will die.
If all electricity and vehicles are disabled in the US, within a short time, most people will lack water and food, and cities would have dangerous sanitation problems. If it is the middle of winter, people would freeze to death in some regions.
So, I think it would be 300 times worse than Katrina (or more than that, if you consider deaths, since about 1800 people died from Katrina in the US, and I suspect a lot more than 540,000 would die if the whole US received a thorough EMP attack).
Even if it weren't, though, even if it were only like a few Katrinas, that is still very bad and very much worth taking inexpensive precautions (inexpensive compared to national-scale boondoggles that the US wastes its money on).
(Also, I'm not considering the effect on nuclear power plants, as brought up above. Maybe they would be OK, maybe not -- I don't know.)