Even when there's a visual frame skip, the game engine is still rendering every frame. Mike Z mentioned this when he proposed that slight game speed increase in SDE.
Er, no. It's not rendering, that's the point.
It just still polls the joystick even if it isn't going to render the frame.
Old games = poll input, advance the game 1 frame, render. If it is on a frameskip frame then = poll input, advance the game 1 frame, advance the game 1 frame, render.
So if you were holding Back you'd be holding Back for 2f, and if you weren't then there was no chance for you to be holding it on only the 2nd of those 'frames'.
SG frameskipped frame = [poll input, advance the game 1 frame]x2, render.
And for completion, games that use delta time instead of 'frames' like FPS's (and I've heard some newer fighters, but don't quote me on that) work by doing "how much time has elapsed since the last game loop update?"
So in normal circumstances
Poll input, advance game world 1/60th of a sec, render.
or if you have a fast computer with no vsync
Poll input, advance game world 1/120th of a sec, render.
etc.
But when there is lag, it does the same thing. Let's say you have a frame that takes half a second to render, you get
Poll input, advance game world 1/2 a sec, render.
Which means in that entire 1/2 sec, you got to provide input exactly once. The game kept up with the lag, but it feelsbadman.