I agree with both of the above - "selected" is a much better idea than "current" (this has even been changed since in the original post), and the RTx series does have a much better interface for changing measurement channel than any other scope I've used.
I often find myself doing a set of measurements on one channel then having to change each one to a new channel though, so I thought it would be handy even given the good existing implementation. That said, I certainly could name a few things higher on my RTB2k wish list (eg more measurement slots, math functions).