I am with you, GF, it does seem odd. Not typed in nor have I flown in one (although our group was afforded a tour early on) but two of our mechs are fully fluent across Boeing's fleet.
My guess would be the frequency wild 235V main AC bus power would not be appropriate for motor operation and high power electronic devices work most efficiently with DC currents. In addition, most of the high power 270VDC loads are variable speed motors and the use of high voltage reduces the conductor size requirements, saving weight.