One problem is that in the most lucrative market, enterprise data storage, the woefully out of date benchmarks that are industry standard mainly promote raw throughput on absurdly large working sets, which makes caching of minimal benefit. Besides inertia, there are some established players who have a lot riding on that not changing, also.<p>Details in this kvetch from Sun engineer Bryan Cantrill (Sun's ZFS-based storage servers do pretty much exactly what you propose, but lose out to NetApp in the SPEC benchmarks): <a href="http://blogs.sun.com/bmc/entry/eulogy_for_a_benchmark" rel="nofollow">http://blogs.sun.com/bmc/entry/eulogy_for_a_benchmark</a>