Apparently George W. Bush has been told not to show his face in public until after the election, because every time people see him it reminds them which party got our country into its current disastrous mess.
That is the last thing the GOP leadership wants people thinking about, since Romney wants to bring back the same policies.
I found it interesting that the Democrats gave the most prominent speaking spot at their convention to their last serving President (Clinton), because he was a massive success in office and presided over 8 years of peace and astonishing economic growth.
In dramatic contrast, the GOP's last president was conspicuously absent from the Republican convention, and as far as I heard was never even mentioned. Translation: "Remember those 8 years of Bush failure? Pretend they never happened and vote to put the same f*cked up ideas back in action."