The Pro: "All of the programs from Reason to Band In A Box can produce "arrangements" of songs, but they are basically sequencers and cannot do what "arranger keyboards" can do."

You're correct. They aren't 'on-the-fly' operations.

I wonder why no one has put in a simple system of chord recognition?

Perhaps one can amend my original post to "ADD one obsolete arranger, and you have a portable solution..."