One frame of latency is not gratuitous; it's perfectly reasonable to not draw directly "ahead of the beam" and instead double-buffer. Otherwise you get a lot of tearing.
I very much doubt the console is watching vsync either.
The extra frame that I mean is: console renders, vsync, compositor grabs it and renders, vsync. That is what happens on X11 with compositing AFAIK. Only one frame time / one vsync is really required before you consider specifics of the software involved. I've read somewhere that Windows also has an extra frame of latency for similar reasons as X11.