your entire thread is based on this statement, do you have any evidence of this statement being true?
so long as your proceeds outweigh your costs (including leases, technology, salaries, marketing, development etc etc etc) you've made money. a game can even do barely more than break even and you're still in the game because you've gained at least the years of salary it took to develop it.
how do you define best-seller?
was world of goo a bestseller?
was nwn 2 a best seller?
gears of war?
torment?
your whole post is just speculation imo
edit: another obvious problem with your inanity is that dragon age is going to be a bestseller, regardless of whether it has dlc or not. the dlc isnt what makes it a bestseller, its the quality and marketing.
the key to making money is making a good game and marketing it, without going overbudget on your costs, dlc is just bonus on top of that, its not what makes or breaks anything