Not all, the one. This is the way AT&T handles dynamic single IP DSL.
You can use PPPoE to assign more than one IP address to a client, however I don't know if the SpeedStream can pass these multiple addresses on. I think this would be more involved.
Not everyone wants more than one machine online. In this case those that do have more than one machine would use a router and can deal with the mess that goes along with it.
