I can answer my own question now. I got in touch with one of the product specialists at SFMC and was informed that the failure of the requestParameter() method was a known bug. It was something that had not been enabled but was fixed with their update on Friday, 1/21/2015. I have confirmed that my code now works.
It is rather disturbing--but unfortunately not surprising--to me that SFMC would sell this product to a client and expect us to deliver a solution with such a basic, major function not working! I believe that when they are actually done with beta-testing this live product, it should support all the functions of the existing landing pages.