I disagree with complaints out there that the MBA upgrades were optimized primarily for battery life, and not performance. As an example, the clock speeds were lowered to further extend battery life - keeping Geekbench performance roughly on par with last year's machines rather than providing the standard 20% improvement.
For one thing, this new Flash architecture isn't something to sneeze at.
But more importantly, I bet you anything the rMBP's are where they will look more to performance. Which only makes sense, as it would continue differentiating the two lines.
And if that's the case, going all-in for battery life is the right decision for their consumer-grade notebooks.
As an aside - 9to5mac anecdotally reports double the battery life on a 2008 MBP running Mavericks. Imagine combining those OS gains with the new Haswell machines!!!