Are you sure that's not because the different teams had different scopes? The iSEC audit was specifically tied to the iOS application.

The scopes had a great deal of overlap; although we (Least Authority) didn't consider the iOS client at all, the rest of iSec's audit has essentially the same scope as ours. The point I was trying to highlight is how easy it is to miss things, and therefore that having independent concurrent audits is actually a really good idea. It would probably be even better if the teams worked mostly independently but were able to exchange draft versions of their reports (before the mitigations necessary for a public release).