When it comes to the first version of an application that you use, you also have to expect that it will never improve and that development could cease the moment you hit the buy button. I think it’s fair to expect that it will function for a reasonable amount of time after your purchase (let’s say a year), but you can’t expect innovation. You can hope for it, but that’s about all. You have to like what you see enough to be happy, even if it never gets any better.
More impact from the Sparrow acquisition. I think Mike says it well. I always consider the developer’s reputation, history and update frequency before purchasing an app that cost more than $2. You can’t expect anything so you have to make your decisions assuming you will never get an update.