Right, nobody pays /more/ than the published prices.
And prospective users can look at the published prices, and see that historically they've gone down more than they've gone up (although obviously that trend could reverse).
So people think they're safe from the risk of Amazon quadrupling their bill over night.
Of course, vendor lock-in can have other negative effects, but apparently people aren't worried about them, or at least think AWS is no worse than the alternatives.
