I've seen them at all kinds of heights.
Reason they want it that height is probably because that's about where the waste water hose comes out of the washer and you want it looped up higher to essentially form a trap (even though there should be a trap in the wall somewhere).
If you are really concerned about it, go to Rona and pick up some pipe to extend it up higher. You'll need a small amount of pipe and a couple of fittings to re-adjust the inlet angles.
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