Southack, you gave a good, simple, logical explanation as to why gravity is faster than light.
I have made a similar simple explanation of why time travel is impossible - where would you stand? As we are always moving, and moving in relation to everything else, being in a different time demands being in a different place.
So, if we wanted to go back in time we would have to back up the earth on its rotation, back it up on it's orbit around the sun, back up the solar system in its rotation, and back up the milky way in its rotation, and back up the galaxy in its movement through the universe.
Somehow I don't think this is possible.
It is very simple: if time travel into the past were possible, you would be deposited in deep space--where the Earth is now--but where it wasn't then.
So that is not a valid objection to pure time travel. If you expected to land in your own house ten years ago, the inventor of the time machine will tell you that your expectations were unrealistic.
However, don't worry: time travel into the past is impossible for many other (valid) reasons.
--Boris