This is where allowing longer legs than otherwise possible (with 2 prosthetics) will lead to an advantage being sought (by seeking out 2 blades, not 1.. or none). As soon as that situation came to light (for example de Oliveira running a WR), I could imagine a totalitarian regime (think East Germany) chopping legs off.. thankfully we've moved past that point now, right?
Bottom line: Paralympians can't 'gain an advantage' on Olympians by having no legs, but merely try and replicate what they are missing. But the IOC haven't defined that clearly enough yet, probably to encourage the growth of the paralympics/fast times/competition.