CNBC is primarily a financial channel and full access lets you watch the network live or you can opt to watch previous clips and episodes. FOX NOW on the other hand is on-demand access to the network's popular shows, including Family Guy, 24: Lives Another Day, America Idol, Cosmos: A Spacetime Odyssey and more. FOX NOW will also be streaming certain episodes the day after theh air through Apple TV.
If you still do not see these new channels, try rebooting your Apple TV to see if they appear.
Apple has added many channels to the Apple TV since its launch, however it is due for a hardware upgrade as the company hasn't released a new Apple TV since March 2012.