Actually, the "high speed" counting part involves a chip that's included in the (more expensive) R1 & EB1 hardware, but NOT on the R2 & EB2s. But any of those PACs can handle counting for your high-density modules, because the not-as-high-speed counting for those actually happens on the modules themselves (rather than on the R1/EB1).
Confusing, perhaps. Arbitrary, no. We don't like to charge you extra for features you don't need.
BTW, if you want to fix the incorrectly configured I/O Unit in you strategy, you can:
- add a new EB2 (you'll need to give it a fake IP address for now, like 126.96.36.199).
- move your points from where they are to the new EB2 (double-click on the "Points" folder under that new I/O Unit in your strategy tree, you'll see a "Move To..." button on the right side)
- delete the non-real R1
- correct the IP on your "new" EB2.
Might save you some confusion in the future!