Both can send bitmaps, but RDP can and does send graphics (and even text!) rendering commands. You can even influence how text is antialiased on the client. And

Both can send bitmaps, but RDP can and does send graphics (and even text!) rendering commands. You can even influence how text is antialiased on the client. And even "dumb" VNC benefits from having more specific damage (as in, "areas of the screen that changed") than just a generic "all the screen changed, here's the new framebuffer, go figure it out".