I think the reason for Sun changing it was due to the advent of NFS, which made measures of process based on I/O blocking inaccurate (and bound to network latency). I believe Cantrill mentioned this factoid at some point, but I don't recall the reference.
As it happens, this isn't the case. Sun introduced NFS in SunOS 2, which unsurprisingly had the BSD view of load averages and did count NFS IO as short-term waits. A NFS server with problems could send client load averages up to monstrous levels (a load average of several hundred was not unusual, all of it from processes waiting for the NFS server) and many sysadmins got to see this first hand at the time.
My point was that the reason for changing it is because of NFS and that it caused sysadmins to become confused. Not that it was changed along with the NFS release.