Hundred Fists tests were done before the Haste cap, and certainly before we realized the "Haste cap" was actually a "Delay reduction cap" that Martial Arts counts towards. Also, they were an approximation because Hundred Fists is a 2-hour ability and it's hard to test. Assuming Hundred Fists is hit by the delay reduction cap, it's not 73% Haste.

480+48 = 528 base delay
300+48 = 348 delay with 0% Haste on a 75 Monk
528*.2 = 105 delay floor
1 - 105/348 = ~70% Haste apparent.

So point is, HF probably does put you at the delay reduction floor.