NOT SIGNED
Everyone seems to be missing the point of what was stated. Future releases of firmware will obviously be different from what we have now, bugs will be fixed, features added, etc. It is entirely likely that something, somewhere, will break a 3rd party app. Nobody is saying that this is intentional, just stating the fact that it's likely to happen. Apple cannot be responsible for making sure that all 3rd party apps continue to run as expected, that just isn't reasonable.
I view that news that 3rd party apps, as they are now, are likely to break as GREAT news. That means that Apple still has loads of things they want to do with the iPhone, improving libraries, adding features, etc.
Windows folks, do you expect all apps built for Windows 98 to run under Vista? Mac folks, do you still expect apps build for OS X 10.0 to run under 10.5?
OS versions change all the time, and 3rd party developers release new versions that are compatible, take advantage of new features, etc. That's how things will continue to be with the iPhone.
When the rumored GSM version of the iPhone ships, will the firmware on this be different enough that it will break some apps? Probably. Look down the road a bit further, this version of the iPhone will at some point be replaced by something better, an iPhone 2.0, or whatever. Maybe a new processor, maybe it'll have GPS, allow for Bluetooth input devices, any of a number of things that folks haven't even considered yet. The apps we have now will probably need revision for the new device.
The iPhone has been shipping for under 3 months, folks have barely scratched the surface of what can be done on the iPhone. Take a look at all the apps that still have version numbers that begin with '0.', take a look at the various hacks and tools that are no longer useful because better tools have come along.
Let Apple do its job and perfect the iPhone, the 3rd party folks will do just fine keeping up.