Why announce App upgrades? Apple already has a mechanism in place to notify users when an App update is available AND ready for download, so your message is redundant, especially when you jump the gun and announce them before Apple has them available for download on iTunes. Save yourself the grief, and leave it to Apple to tell us.
It's our experience that not all potential customers look at the App when it is updated. If you haven't purchased the app, you have no easy way of knowing what is being fixed and updated. We post here because some customers may be waiting for a specific feature to be implemented (such as the iPhone support). Regarding jumping the gun, our policy is to post when we release the app to the App Store. It takes some time to process the app and we notice that different stores around the world get the app at different times, even when we have released it here. So, we do the best we can and try not to jump the gun too far!