> need to implement

I think "need" implies too much. Because, for example, for 100% headless applications the open+free version is already viable. (But in practice everyone wants to debug using the HDMI from time to time, mostly because almost noone has NTSC lying around.)

Also, without looking at the docs of the VPU, I'd guess that most of the blob functionality is needed for advanced vector stuff and whatnot (so it's only needed if you want to implement OpenGL/EGL/WebGL).