Most IP cameras support SD cards and we've covered this SD Card For Surveillance Tutorial, First Surveillance SD Cards Released (SanDisk), Embed SD Cards inside IP Cameras? and Edge Storage Usage Statistics.
It can be done, it's just not widely used, primarily because of weak overall VMS integration and limited demand (most people are not that worried about a recorder being stolen).
It sounds good on paper.
IPVM has done reports on the lifespan of an SD card when written to constantly and it isn't pretty. Some of the cameras monitor the storage and can output a message when the SD card has failed. Otherwise, how would you know?
New NVR's also provide PoE to the camera. Unless a separate power supply is run to the camera, when the NVR is stolen, so is the camera power so you only have video to that point. Maybe it's enough, if the camera allows multiple power inputs at the same time.
Imagine having to replace a few hundred defective SD cards, in the cameras.
Several times a request has been made for "cloud storage' or a second NAS and other ways to combat this issue. Some just put a dummy DVR/NVR in plain sight.
depends right now I have an edge storage software i have been working on for Linux OS's works really well just mirrors what on the SD card to a NAS, lots of logging, lets me know if they (camera or SD card) are down or out , and lets me look though all of the uploads in a decent manner.
so far the SDXC cards last about a year outside and just a little longer inside, but this is using the higher quality class10/UHS-1 cards. I will say I notice a big difference between regular SD cards and the micro SD cards, as the SD card last about 6 months on average.
then again the only cameras i have tested with SD cards so far are Panasonic and Samsung, I have heard some horror stories with the AXIS cameras.