> I want my presentation software to have a set of features and then never change until I make a very deliberate act of upgrading to a new version while still having the old one around in case I get stuck.

Note that I'm not using the App Store for distribution, I'm using Sparkle, which means that it never updates without you allowing it to.

Also , if it's a dealbreaker for a lot of people, it would be trivial for me to make older versions available for download! (I keep them all, and this has come in very useful on some recent support calls).