Yes, I certainly agree and as you say Interoperability is a wonderful thing! However, that is highly dependent on that ALL camera manufacturers follow the standards. Many of them follow to a certain extent and then they do some extra stuff that messes up. We have been looking into onvif PTZ and so far many have discovered that it depends on manufacturer. Many manufacturers do the whole product line with camera-nvr-software. Doing so they quite often make features that only work in their own system. When producing cameras, software etc. you must also know who your customers are or will be.
I would say that this area have been around for some time, but during the last 2-3 years it has evolved quickly and it will continue to do so. I went to the website above and onvif is specified on some cameras, but what really is included in the onvif I cannot find.
However, it certainly looks very interesting and if you continue please report back if you find a lot of goodies included in the onvif standard.