You're right about the airflow traps preventing the heat transfer out at night. However, I think windows will trap the heat from incoming sunlight as well as the black vanes since a window allows the light to reach farther into the building and get absorbed by the floor (or opposite wall). Ultimately he wants the heat in the floor anyway, so it's best to get it there via radiation. Not much of it will be radiated back out the same window. In fact the black vanes and the rest of the collector should radiate more of the energy back out to the world because they're hotter than the interior space.
The key difference between windows and the solar panels, as designed, is the passive design of the solar panels. No need to close curtains on these panels, as windows would require, for reduction of heat loss on winter nights.
The black vanes are cooled, during the day, by induced air flow, such heated airflow going into the building (passively), and results in heating the building, without further action. The panels are designed to prevent winter-night cooling via the panels. Thus you're missing the passive intent heating intent of the design: windows fail as a passive heat source, because of the need to actively insulate them in some fashion in the winter night.
