Ya know, looking at that, imo that's probably about right.
Those two components will have the most influence on the performance of any machine.
It's all very well to say 'you need all the parts for it to work' (which I actually have said ) but if we are to view the original question as to which parts are the most important, which could mean will influence a machine's performance the most, then it has to be the Motherboard and PSU. Definitely not worth skimping here.