From my understanding the FCC's power limit is what is keeping reception from being the best that it can be.
I am not positive, but I would wager that all things considered that the receptions should actually be the same on all models of HD Radio under the same conditions (i.e. same antenna, placement, and such.)
In response to fmdxer333, a portable, at this moment, is not feasable. The HD Radio module and DSP require too much power and therefore prevent it from being powered for a reasonable amount of time using current batteries. I am again, not sure how much I am allowed to divulge about the technology, but I understand that iBiquity and other companies are working on it and expect to have the module in a portable form in about 18 months. We already have a product designed waiting for this to happen and will hopefully be the first to product a portable HD Radio.