I don't think this is really a counterexample. skype was already a widely used product when microsoft bought it. joel isn't arguing that you can't have enough money to just buy a product that already has a large network of users. also (iirc), skype only took market share from aol in the first place because it had a killer feature aol lacked: video chat. network effects mean you can't be replaced by a similar service, not that you can't be disrupted by a new product with a unique feature that people actually want.