Just to clarify, previously dead applications were resurrected by a change in OS X, not through an update by the developer?
That's exactly what happened. (One of the apps has even been abandoned for a coupl'a years.)
I've noticed that the icon for dead apps has a circle with a slash through it overlaid on the icon. It should be easy to spot that change if the application is now functional.
I've seen that icon in situations described by joemike, as well as in instances of OS X version incompatibility, although that's not universal; it often takes trying to launch an app to learn that it's incompatible. (Edit: There was, however, no such icon associated with either of the two resurrected apps.)
I just went through my entire app collection and double-clicked every one of them to see what would happen, and I was pleasantly surprised.
