I'm pretty sure that ESAPI doesn't "meet" Level IV criteria only because it uses a different criteria. I think it stops all level IV threats, but is rated for multi hits. It would actually be a tougher/better standard than level IV.
From BulletProof me, about 2/3 down page:
Similar to NIJ Level IV
The E-SAPI test is very similar to the NIJ Level IV test, but just a little bit tougher. The mil-spec calls for the plate - with an Interceptor vest supporting - to stop one round of .3006 AP, just like Level IV.
But it must also stop a second round, 60% of the time (not 100% of the time - too much of a weight penalty).
ETA: the reason people on here "want level IV" is because it is better than III and we (I) can't afford true ESAPI plates. I'd prefer ESAPI, but for the price difference IV is plenty good for my needs.