LH423, I think you may have missed the first option. When performing a search on that particular flight, the results came back to me as follows:
Departure, Arrival, Flight Number, Stops, Transfer Point
15:10, 09:25+1, LH728, 1
13:05, 09:25+1, LH4444/LH728, 1, Brussels
07:15, 09:25+1, LH4466/LH728, 1, Brussels
09:05, 09:25+1, LH4428/LH728, 1, Brussels
So the way I see it, you *can* take connecting flights to Brussels, but you can just as well go on the B744 and have one stop, being the one at Brussels.
Whichever way, they obviously won't be flying the jumbo to Brussels on a ferry flight.