You always hear about great defenses being able to create pressure with JUST their front 4. Obviously this enables the 7 others defenders to play blanket coverage, whatever scheme that may be. I believe that the coaching staff truly believes that they can create pressure on third and long with just their front 4, ie Irvin, Jones, Branch, and Clemons. They aren't willing to take a gamble and bring an extra blitzing defender, particularly against good QB's. Well thought out!
It isn't working, however, on the road. The coaching staff needs to wake up and start getting more creative and taking more risks with blitzes and pressures, and not just in the second half. Let's face it, Irvin is good at home, but he's a complete non factor on the road. The coaching staff should have adjusted their calls after they knew Jones was out.