I would guess they did so in the same way that google asks every website operator before crawling and caching. (I.e., I suspect they didn't come to any explicit agreement. If google doesn't, why should they need to?)
This is probably the wrong attitude towards founding startups. In general, you shouldn't unnecessarily risk the business -- but if people are throwing roadblocks in your way, lots of startups seem to generally do pretty well when they play fast-and-loose with rules. The logic is that nobody's going to bother to sue you until you get big and can defend yourself. Obviously taking a big risk like this isn't ideal, but you shouldn't let it stop you from moving forward with a business.