External cups/bearings costs less. I will swap my heavier/better sealed/longer lasting (but more expensive BB) for lighter , less lifetime , easier to work with and cheaper BB's. A 9 speed DuraAce BB will cost you easily $100 or more (not saying that you can't find them cheaper but I do know how much Shimano in Irvine ,Ca. will charge your LBS for the BB and then your LBS has to make some money. The 10 speed DA BB will cost you $50 and maybe less at your LBS. So the bottom line is -- I will swap to a less durable product as long as I can get great performance out of it and at 1/2 the cost.