You lock it down you gain a competitive advantage. You buy yourself a few months leeway while they are hacking away trying to clone your device. As was said earlier, if you don't do that they may even release a clone product before the official product itself launches.
I do not necessarily agree with the Release Early, Release Often for all software though. For one I wish KDE 4 had not come out until it was up to standard with KDE 3. Too many distros have adopted KDE 4 and practically dropped KDE 3, when 4 is just not ready yet. Had it not been "released early" they would have stuck with 3 that bit longer and avoided the ton of teething problems people have with 4. I get it, you need people to test it. But surely there are plenty enough people willing to risk early software rather than forcing it onto an unwilling public. But this is getting off topic.