Anyone from the community is welcome to help to update the packages, etc. – not just the maintainers of the respective packages. A beta version for 4.07.0 was announced on April 13th, and a release candidate on June 19th, for a release on July 10th. There was some time to check the packages that you care about before the release, and maybe lend a hand in upgrading them. And you can still do it now!
The core team that takes care of the release process usually checks for breakage on opam (this corresponds to package that are marked to be compatible with the upcoming release but fail; packages that have a lower version bound are not tested). But with most people working on a volunteer basis, it is hard to expect much more, in particular now that we are aiming for time-based releases – so when it is time to release and when we have made a decision on all known bugs, well, the release gets out.