0.00009999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999 is not = to 0.0001 ... (just kidding)
Here's my guess: 10^ with a positive integer exponent is computed by repeated multiplication, so it gets an exact answer. Or maybe that's true only for small positive integer exponents. For any other kind of exponent, it uses an approximation to an infinite series, so the steps of the computation are different.