Most people aren't aware of what they are missing and how it could bring a great deal of benefit.
This isn't about NFSv4 (the filesystem), it's about the rich permissions model it standardised which is now used by more than just NFS. It's used by ZFS, and it's used by the FreeBSD and Solaris VFS, and likely others as well. It's the only rich ACL model in real use today on open platforms, and being a superset of both POSIX.1e DRAFT and Windows ACLs, it's needed for full interoperability between platforms.
Samba doesn't "work fine" except for the simple case. Using it with groups and group permissions can be exceedingly painful. When I export a ZFS filesystem on FreeBSD over Samba, it exposes the full ACL model to the Windows client which is accessible and manipulable via the standard security properties as well as the command-line on the server or and NFSv4 clients.
When working with group permissions locally or over NFSv4 or CIFS, you aren't restricted to the pitiful group and setgid permissions offered by the standard UNIX permissions or even POSIX.1e ACLs. You can add an @group ACE detailing the group access permissions and their inheritance, or custom ones per user, which can make working on shared data much simpler. No more pain when someone with a broken umask adds something and strips off the group permissions, or they drop the setgid bit and the inheritance is lost, or they access it via samba and it sets the wrong group ownership or permissions. All of which I see regularly on shares exported from Linux. We often have to export the same share multiple times with different configuration to work around the limitations (read-only, group and group perms), where if it was using proper ACLs just one would work for all cases.
However, your first sentence is valid for many things, not just ACLs. For example, there are people (ehm, me) who value being able to have Kerberos tickets for multiple principals from multiple KDCs at the same time. This is something that the most popular OS (Windows) is not able to do - and nobody minds. Because for most people, being part of one domain is good enough.
With ACLs, I find it similar. For most people, the complexity is too high, the reasoning about them so complicated, so there's no benefit to have them available, they won't use them anyway. Also, in our case, we just have multiple groups at the root of samba share and that's it. It is good enough. So maybe it is yet another case of worse is better.
This isn't about NFSv4 (the filesystem), it's about the rich permissions model it standardised which is now used by more than just NFS. It's used by ZFS, and it's used by the FreeBSD and Solaris VFS, and likely others as well. It's the only rich ACL model in real use today on open platforms, and being a superset of both POSIX.1e DRAFT and Windows ACLs, it's needed for full interoperability between platforms.
Samba doesn't "work fine" except for the simple case. Using it with groups and group permissions can be exceedingly painful. When I export a ZFS filesystem on FreeBSD over Samba, it exposes the full ACL model to the Windows client which is accessible and manipulable via the standard security properties as well as the command-line on the server or and NFSv4 clients.
When working with group permissions locally or over NFSv4 or CIFS, you aren't restricted to the pitiful group and setgid permissions offered by the standard UNIX permissions or even POSIX.1e ACLs. You can add an @group ACE detailing the group access permissions and their inheritance, or custom ones per user, which can make working on shared data much simpler. No more pain when someone with a broken umask adds something and strips off the group permissions, or they drop the setgid bit and the inheritance is lost, or they access it via samba and it sets the wrong group ownership or permissions. All of which I see regularly on shares exported from Linux. We often have to export the same share multiple times with different configuration to work around the limitations (read-only, group and group perms), where if it was using proper ACLs just one would work for all cases.