Axiomatic Unicorn: I disagree with your characterization of the EWM. If the only abilities of the class related to fashioning/improvising weapons, your case would have a bit more force. However, the EWM gains focus and SPECIALIZATION in a vast array of extraordinarily complex and often difficult-to-use weapons. The duom, spiked chain, whip, kusari-gama, elven thinblade, and three-section staff are not weapons that demand an "improvise anything" fighting style; they are complicated weapons that take time and effort to train with beyond the scope of a fighter's martial training; hence the EWP requirement. Believing that a barb (or any other character) can become super-skilled with these weapons simply because he has an unorthodox fighting style that allows him to grab just anything and use it as a serviceable weapon is a bit of a stretch, IMHO; though I guess it's a better explanation for the class's current requirements.
IMC, the EWM has the following prereqs:
BAB +5
EWP and WF in any two exotic weapons
Proficiency in all simple and martial weapons