I don't think the offense has never held the edge in payroll even with Carr in the equation. The only guys beyond their first NFL contract on the offense are Wade, Wiegert, McKinney, and Bruener (who isn't breaking the bank).
On defense you have guys like Sharper, Glenn, Coleman, Payne, Wong, G Walker and Robaire who have some of the biggest $$$ contracts on the team.
The offense has been built through the draft (for the most part). THe defense has been built through the expansion draft and free agency (for the most part). Since a lot of our offensive starters are still in their first NFL contract, it follows that they aren't (yet) making the big dollars as a unit. That will change as time goes on and it will level out.