Given those choices, I'd say the product line, but its more than that. For example a product like this does need 3rd party support in the form of app compatibility with its unique features, such as dynamic switching, and more importantly it needs accessories like cases and the like. If the buzz on the Padfone becomes established as dead on arrival, 3rd parties will not invest in supporting it. The longer it takes to come to a wide market and the story can be turned to positive reviews and sales numbers, the more likely the DOA tag will stick. That will kill it in terms of sales.
I've had DOA devices before, like the HTC Athena and the HTC Shift. They were not particularly happy experiences because they did not sell well and HTC didn't give it much support. I never found a decent case for the Shift before I sold it, for far less than half the price I paid, I would add. Keeping it old school, compared to the HD2, the ownership experience is night and day with support for tons of roms, apps, a plethora of accessories and general market support pricing accessories cheap and so forth.