The 8.1 Camera Roll is somewhere between "old" Camera Roll and "Recent Activity". It is exactly like the original Camera Roll in that it shows the photos taken by your iOS device - all of them back to the dawn of time; and nothing more. "Recently added" showed only 30 days' worth of photos, plus it delivered a photo stew of your native shots plus Photostream plus (I think) anything else you'd imported to the device within the preceding 30 days.
In this regard the 8.1 Camera Roll is just like the original.
The difference lies in deletion. The original Camera Roll only showed photos taken by the iOS device, and, when you deleted them, only deleted them from the iOS device. Photostream stayed as it was. By contrast if you deleted something from "Recent Activity", it would not only delete the local version but the Photostream version as well. In the 8.1 Camera Roll, deleting a photo deletes the Photostream version as well. In this regard, the 8.1 Camera Roll is exactly like "Recent Activity".