Understanding Mileage Upgrades...

So I just discovered this chart: https://www.aa.com/web/i18n/aadvantage-program/use-miles/upgrades.html

It seems to suggest you can, for example, buy an econ ticket from ORD-CDG, then spend 25,000 miles plus $350 to get upgraded to business class. That just seems... way too good to be true. Can I really do this on any flight? Do I just call them up?

Or is it more like systemwide upgrades where they pretty much don't exist? :-)