Remember, the R22 originally had a 1300lb limit and was pushed up to 1370lb for the Beta without, as far as I know, any structural change. When asked the question many years ago, Frank said it would mean beefing up some of the structure to maintain fatigue criteria, which would mean stronger drive train to support the extra weight and so on. Law of diminishing returns and why Robinsons would prefer people to use R44's, which also have a greater profit margins I suspect.