Subwoofers aren't directional, so the orientation of the subwoofer driver does not matter one bit.

This is not entirely accurate. No sound waves are inherently "directional". You can, however, create standing waves by facing any speaker directly at an acoustically reflective surface. If you have an 8-inch driver facing directly at the floor or against a wall, you will end up with distortion at certain frequencies, so creating an angle to mitigate this can do wonders. While the orientation of a sub matters much less than other speakers for what YOU hear, proper placement can have a big impact on distortion and sound bleed for your neighbors.