Two things I do understand and the first is that it doesn't take multiple thousands of employees to market a single drug...in fact not even close..
The second is that most biotech companies out there either partner their drug prospects at a point or they take them to market in house and simply hire the people needed to do that. They don't go about a process of creating a new costly company that requires all those added expenses as described in Iyonwin's post and some of mine in the past...
IONS had at first stated they were creating a division to bring a pretty good group of drugs directly to market then backed away and partnered the best ones to Novartis.