To me, the confusing part is why NBC only lets cable subscribers stream the content for free. I would guess that the cable companies are paying them to do that, but that is pure speculation on my part. If I can stream everything online, why would I purchase cable?
By confirming your cable subscription, you confirm you have access to MSNBC, CNBC, and Bravo, where the majority of Olympic events are broadcast. Only a small number of events are broadcast on NBC affiliate stations, mostly only in primetime.