This is correct, the most common way to get a stream from a camera is to pull it from the camera using a pullStream command. This is almost always via RTSP:
pullstream uri=rtsp://IpofCamera/streamname localstreamname=mycam
Your camera must have the ability to push a stream to utilize the "push in" functionality of the EMS. I am not familiar with any off-the-shelf cameras that have push RTSP capabilities.
However, we have partnered with a few different companies to integrate the EvoStream Media Server onto their cameras. This provides a whole suite of tools including the ability to push both RTSP and RTMP. This allows you to push out of firewalls with no configuration to either an EvoStream Media Server instance in the cloud or even directly to a public CDN like StreamGuys, UStream, Akamai, etc.