Yes, it is disappointing that all H4D cameras cannot be upgraded. However, that is not an exclusive situation with Hasselblad only.
What Hasselblad did do is offer the amazing H4D camera in a version that more people could afford ... by using a previous digital back that successfully had been in production for some time (H3D/31 and H3D-II/31). For that reason, the H4D/31 was/is considerably less expensive than a H4D/40 ... $6,000. less in the USA. The difference between the H4D/31 and H4D/40 that both have the same sized sensor, isn't just 9 additional meg. The 40 sensor is all new technology. Hasselblad does not make the digital sensors, Kodak and Dalsa do. Then Hasselblad engineers backs to maximize use of those new sensors. So does Phase One, Leaf and Sinar.
Unfortunately, that older 31 digital back technology was designed and produced before new feature technologies were available. The 22, 31 and 39 digital backs do not have the physical hardware to accommodate the features of the new firmware upgrade.
Hasselblad DID announce sometime ago that the newer digital backs would eventually be able to be have a higher resolution LCD and some other features, available through a firmware upgrade. They were very clear that those features would be for the H4D/40, 50 and 60. The first H4D to get them was the H4D/60 ... and now, as of Dec. 1, 2011, they will be available for the 40 and 50/50MS/200MS backs. While a bit slow doing it, they are simply keeping their promise to those who bought those 40 and 50 meg cameras.
The 31 is a well proven back, and the fact that you can have it on a H4D body at a more reasonable price is terrific IMO.
-Marc