Mostly true, except for the Mojave Green Rattlesnake, a truly nasty, dangerously neurotoxic critter. See:
http://en.wikipedia.org/wiki/Crotalus_scutulatus
The Southern Pacific Rattlesnake is another viper you want to avoid; venom is similar to the Mojave Green. I’ve watched a few episodes of “Venom ER” where individuals bitten by a Southern Pacific rattler were treated; the amount of anti-venom required is often much, much higher than the dosage for other snake bites.
Didn’t know those existed. Looks like it would make a lovely pet!