I put the question to my equipment provider, and he was very surprised to hear the "every two weeks" suggestion. He would recommend replacing every 4-6 months.
I am having no issues with my Nuance pillows (after a few false starts) during two months of use. They work well for me, although certainly best if I sleep on my back.
I wash the pillows religiously every day, and hang the tubes up to air dry. I did appreciate the suggestion from Sleepster not to use water that is too hot!