Just to add to EPD's comments, 29mm (which I hear the Hasselblad '28mm' actually is) on a 48x36mm sensor is equivalent to 34mm on full frame 645. In other words, when a 645 sensor becomes available for the Hy6, the 35mm lens will give about the same FOV as the '28mm' on a Hasselblad.
I think the HCD 28mm for H is purposed designed and built for 36X48mm sensor, so in its perspective a real 28mm lenses, when mounted on a full 645 sensor (or 94% full frame 645 sensor), it is a wider than 28mm but with a image circle not fullfilling the frame, I believed, and it is why 28mm lens is quite a bit smaller than the HC 35mm. The Mamiya 28mm is more honest 645 format lens but on today's 36X48mm sensor it is wider than labeled on the lens. Hasselblad itself said the 28mm is a lens design with digital calculated in mind, so it can be produced smaller, and faster. The image from the HCD 28 is a very good and sharp, and only very close focus that still exhibits sight distortion - even with the digital correction, but it is quite good enough. I guess they are competing in this regard to common medium format DSLR, not those offering from Rodenstock and Schneider on technical camera, and especially the ArTec - which is probably the new standard for wide angle lens work today and certain can support true 645 sensor. It is a camera on many photographer's wish list.
