These Mobos are designed to provide stable suppliers to all of the PCIE slots (more than previous Motherboards - which are already decent). The 3 ATX supplies means you're effectively building 3 Rigs but only need one motherboard to do the job that you'd usually need 3 (plus 3CPUs and RAM) for.

Yes - you would use USB risers to place the cards in better positions for space and airflow - not in the slots directly.