I've never understood this thought. Any random opportunist won't care if it is a $50 Huffy or a $6000 Cervelo, so long as they can quickly turn it around for a couple bucks or make use of it on their own. Any true bike thief will be able to spot the components, and barring that know that something that looks like an exotic metal and weights nothing is probably valuable. In any case, even what we'd consider a cheap fully loaded tourer in most parts of the world is going to be an expensive oddity worth grabbing if left unprotected.