If you want to keep everything for future use on a non-OSX machine, you can select the iPhoto library file (last two versions are single files; earlier versions are folders) and choose "Show Package Contents". You will see a whole folder structure with originals, modifications, and so forth. You could select everything and create a zip archive.
This would require a bit of work later to figure out exactly which picture is which (since the iPhoto database would be unreadable), but you would have everything.
The method of going through each event and exporting would be time-consuming, but it seems that the issue becomes one of spending the time now or spending it later.