You make several valid points, but I don't want to go on ad nauseam about what Garmin should and shouldn't do to keep me happy. They do what they do to keep their shareholders happy. I've only speculated from the sidelines as to why they're doing what they're doing.
Back on topic, there is no technical reason why Garmin has to impose such limitations in the GPSMAP 640 as they have, not to mention such an artificially inflated price tag ($1199.99 USD MSRP; who are they kidding?). They are protecting their market so you have to buy another device instead of having the "one size fits all" GPS.