There is no rule stating that the electronics must be covered. The only statement is that teams should design their robot to withstand vigorous interaction, that is, to make it robust.
However, let's break the problem down:
Cost of victor 884 speed controller $115
Cost of Robot RC $565
Cost of Spike $35
Cost of radio modem $150
Add to that cost the anxiety of trying to replace those components before your next match
vs:
Cost of 1 ft by 2 ft sheet of 1/8 inch thick lexan from McMaster-Carr $ 8.70
Value of Knowing your electronic will not get smashed to bits: Priceless
PLEASE PLEASE PLEASE protect your electronics. They make your robot move. Be nice to them. (No magic smoke either)