For anything that involves electronic parts, manufacturers need a "Made foriPhone" or "Made for iPod" certification in order to be featured by Apple, the application for which costs just several hundreds of dollars each time.
See the non-existent MadeForiPhone accessories market -- accessories with their own electronics could have an 8-18 month lead time, so we still probably won't be seeing the first proper iPhone add-ons until closer to the holidays.