Absolutely. But the existence of the product doesn't prove anything the same way that the existence (and success!) of the Tik Tok[1] doesn't prove that Apple should have been competing in the "wristwatches that play music market".
Except Apple responded directly to the existence of the Tik Tok. They sell it in their retail stores. They referenced it in their media event. The first highlighted feature in their last update to the iPod Nano was "new watch faces". The success of the Tik Tok (and more recently the Pebble watch) proves something. Likewise the existence and success of all these keyboards for the iPad (thebrydge isn't the first and it won't be the last) proves something.
[1] http://www.popsci.com/gadgets/article/2011-05/record-breakin...