Interesting results! My attempt to explain:
If you pitch enough good healthy yeast, fermentation temperature doesn't matter so much. Try this same experiment with a poor pitch of old yeast, and you will get very different results.
Also, I am absolutely certain that selection of the specific yeast strain can make all the difference. Try the same experiment with a hefeweizen yeast or Belgian yeast, for instance, and you will get two entirely different beers, no matter what your pitch rate.
But USUALLY... if you pitch a lot of healthy yeast, this can make fermentation temperature closer to a moot point.