It's the cross-border confusion of the Innanetz again.
The Plus is from a naming convention Festool uses in Europe. Festool America does not follow this naming convention, probably because they offer a limited range of products and packages compared to Europe.
So the Plus only has meaning in Europe and not in America.
It works as follows in Europe:
OF2200 EB = Router only, with the most basic necessary accessories like a collet, wrench and dust collection hood.
OF2200 EB-Plus = Like above but now in systainer.
OF2200 EB-Set = Like above with systainer, but now also with (often costly) extra accessories.
So in Europe when you want to buy a tool you can choose between several packages and the Plus and Set extensions tell you which is which.
But in america they don't have all these different packages, so the naming convention is not so useful there. For instance, almost all tools come in a systainer in America, so no need to use the Plus to say it comes in a systainer. In fact, if they would use the Plus, it might add confusion for the customer, because there is no basic package to "Plus" from.