Your Nexus 7 may be part of a bad batch? Wireless Charging DOA.

My new N7 doesnt charge using Nokia DT-900 charging plate. After research, others have same issues with varying charging plates, pads, orbs, whatever...

http://forum.xda-developers.com/showthread.php?t=2380155

Users who have complained that Wireless Charging not working on their new N7s have returned at Best Buy for another N7 and confirmed Wireless Charging does work. Case of bad batches of N7s with faulty wireless charging?

If you plan on using Wireless Charging in the future for your N7, you might want to test if yours works.

Same thread also confirms wireless charging of N7 using Nokia DT-900 does work.