This from the I-131 instruction document seems pretty clear:

If you stay outside the United States for less than 1 year, you are not required to apply for a Reentry Permit. You may reenter the United States on your permanent resident card (Form I-551).

I'd take this, along with the advice from Immigration, cbp, andyour congressman, and call it the answer, rather than a random comment from one individual board agent.

Your wife might want to have a copy of the brochure with her:

http://www.uscis.gov/files/form/i-131instr.pdf