For some perspective, here's something very similar to the supervisor circuit on my Dell ATX power supply. And this is from a Dell desktop that's like 5-10 years old. As you can see it's monitoring current AND voltage on 5 outputs (3.3, 5, & 12v). It checks overvoltage, overcurrent, and undervoltage.
And it has protection on the input (fuse, MOV's, PFC, etc.).
So blowing up really isn't a reasonable likelihood, nor is destroying the motherboard. Hence my skepticism.
Of course that won't stop the anti-ATX fanboys from jumping to the assumption that these ATX supplies are just crap, but anyway...