Having stumbled upon this question (and answer): https://stackoverflow.com/questions/2170843/va-virtual-adress-rva-relative-virtual-address on my quest for understanding Windows' PE format, I'm wondering: why is the default imagebase value 0x400000? Why couldn't we just start at 0? A VA would then be, in all practical purposes, equal to an RVA.
I'm clearly missing something, but I've been unable to find a reasonable explanation of this for the last 40 minutes.