A lot of misinformation and guessing in this thread...
First of all, if you turn on iCloud Photo Library, your camera roll is NOT also backed as part of iCloud Backup. Why would it be? As many of you say, it would be redundant and double taxing your storage.
Instead, when you restore from backup or setup a new phone, your entire Library will appear on the device, as it should, without ever having been part of the "backup" itself.
Second, all of these iCloud services take up the same storage allotment. Apple is not going to store your entire Library of photo and video for free. They have, however, introduced fair pricing for iCloud storage, so that its now possible. The cost is measly, and your data is actually safe from loss. I am excited to get my entire library stored once the Mac Photos App is finally released. I could spend a lot more on RAID systems and duplicate drives and safety deposit boxes......no thanks....iCloud Photo Library.....automatic, secure, and easy....worksforme.