Yeah, we all have alot to complain about with Apple these days.
This is always an issue, anytime you upgrade your software. I'm always getting asked about upgrading my projects when for example I open a FCP5 project in FCP7. Since I'm never going back to 5, it's a no brainer, however there have been times when I save a copy of my FCP5 project. Events are different since there can be media and more in the event folder.
Since there are things like multicam clips and roles that didn't exist in 10.0.0, it's easy to see why they had to change it.
I recommend the upgrade however, and then the newer format on the older application won't matter. Especially since it's free.
And if this is who I think it is, it's been a long time since Madison. Fancy running into you in a support forum.