The author might consider using Microsoft products because they are obsessive about providing backwards compatibility. That's one of the positive things about Microsoft products. The downside is that they have to deal with a lot of old baggage as a result. Apple, on the other hand is almost the opposite. They're obsessive about upgrading everyone and leaving the past behind. That's great because they're free to make…
The most important point here is that if you are aware of the problem and provide an incredibly lame dialog to deal with it, then you should have just provided the solution. Clearly Apple has all the necessary tools in their possession to fix this problem: they own the source to both Keynote '09 and the latest Keynote. Why not either 1) make a small conversion utility and provide a direct link to it in the dialog (still lazy but at least actionable), or 2) include said utility as part of the latest Keynote so you don't have to show a dialog? We're not talking "backwards compatibility philosophy" here, we're talking user experience 101 (something Apple used to hold in the highest regard). This is particularly important given the context of the software: certain file formats are expected to stick around way longer than others. In particular, with presentation software there are loads of class slides sitting on the internet that probably will never be updated, which means you are often putting the onus on someone who didn't make the file to go and convert it. Compare this to, say, Final Cut where the only real client of the serialized file is probably the original creator, and it is thus more reasonable to expect a higher degree of personal responsibility in keeping it up to date.