.. and i don't think this is related to framebuffers.
Ultimately it is... (almost) all higher level code eventually falls through to it (EGL, OpenGL, OpenVG, OpenGles, CGL, etc usually are built on top of it. Even X11). I refer to it because the fbdev is already vsynced in many cases (by necessity!) at the kernel driver level , but it depends on videocard hardware: even with fb tearing can occur.
I will add an example to the wiki. Also direct rendering.