The NRL were clever in a few regards. Firstly, to get the deal done before the AFL started negotiations, even though they were off contract first. With the AFL being a 2 horse race between 7/10 consortium and channel 9, if one of these parties were to get the AFL, league would have gotten a rough deal from the lack of competition. This way, Seven were very interested, Channel 10 flirted with the idea and Nine obviously were prepared to pay more than double than they did perviously. This also makes things interesting for the AFL, Channel 9 have their hands tied with League, at least financially. They probably wont make a serious attempt to keep the AFL, meaning the 7/10 consortium can pick it up for chips.
There have been questions asked over the length of the deal, some say 2012 is too long. IMHO, it's a smart move. The NRL is owned effectively by it's broadcasters for the next 8 years. In other words, the NRL have their money, whether league does poorly or not, it's only the broadcasters with something to lose at this point. With seven years under their belt, they will be left with no choice but to make the NRL increasingly prominent in order to cash in on their commitment. This means publicity in the emerging states. This is obviously also very good news for the NRL. Over 8 years, they can build the popularity of the game to new levels.
Another positive over the length is the fact that the Digital recording system hasn't been fully implemented in Australia yet, when it does, it will most likely change commercial TV forever. Being able to skip ads is dangerous ground for FTA networks who make their money from advertising. If adverts aren't being watched, no company will be willing to foot the bill and will obviously make many shows redundant. By locking in the deal for now, the NRL are basically assuring substantial funds through any adverse situation that may arise.