This news will certainly lead to big business. There are a long list of reasons why Apple would change their position on this

  1. Establishing a point of parity with competitive app stores. Facebook in particular is seeing enormous companies built on their platform and the sale of virtual goods.
  2. Leveraging their strongest asset: a billing relationship with millions of customers to make the economy larger and more profitable.
  3. Pirating of applications was rampant.

Talking to a few people at Apple, no one realized how large this economy could be. With the market coming to them, changing their stance to take advantage of the enormous wave of innovation pushing the platform forward is a no brainer.