UPDATE: for those of you that might be a bit confused by this, let me try to explain. the inside hole of a skateboard wheel does not actually touch anything. it is the bearings that are pushed into the wheel that spin on the skaeboard truck axel (see below image).
hence, the shape of it (which is pretty much always circular) doesn't actually matter. the manufacturers might as well keep it circular though, because once the bearings are pushed in, no one will ever see the interior shape. and that is why i like this design: pointless but fun!