Distributed mining is the defense against attack.
Which implies that it needs a defense. Sans that it can be brought down. Governments can ban GPUs, mining rigs etc. so the defense gets weak while they can have powerful hardware.
What does the technology have to prevent such a thing from occurring?
Bitch please, ban computer parts?
They don't need to make a PC revolution to make a 51% attack, they have lots of super-computers to make a lot of floating points operations that, if they want it today, they can make the 51% attack.
Not really.
There are super computers, but generally they are already committed to tasks other than fucking with bitcoins and floating point operations also don't have much to do with SHA-2 hashing. There isn't a single supercomputer that could 51% the bitcoin network on its own. Traditional and even newer GPGPU supercomputers are actually a really shitty way to attempt a 51% attack.