ESRI is really pushing hard on proliferating their own PROPRIETARY services with their 9.3.x Server offering and recommending this over standards based interoperable web services to the GIS community "at large".
I am also PUBLICLY stating that thier support for the OGC services (especially CONSUMING them in their clients) is VERY WEAK functionally as a feature set and the performance is very, very poor. The ERDAS APOLLO Image Manager Web Client is such a better user experience and faster at consuming OGC services than ArcMap!!
Lets put ourselves in their shoe's and dwell on why this would be??
ESRI currently holds the largest marketshare in the GIS domain. They have every intention to keep that marketshare. To the market leader, making the OGC services actually work equivelently to thier proprietary services does have the possibility of marginalizing and commodotizing feature sets in the GIS market leaving "opportunity" to those who are supporting the interoperable services. Forcing the customer to "have" to use proprietary services and SDK's to meet thier use case is also in ESRI's interest as it requires vendor lock-in on the server and client side. It's quite easy to say that the OGC services aren't "rich" enough to provide the use cases that clients need when thier only experience with it is extremely limited and the performance is very slow (as experienced in thier software today). They also have no interest in a "governing" body controlling technology decisions and/or application profiles on the technical side.
OGC Services on the other hand need to provide the user experience and the PERFORMANCE that proprietary services do. In my opinion, this can only be provided by the geospatial vendors. The open-source project don't have the wealth of domain experience, existing codebase and market experience to do this. They of course will provide a user experience, but at a very poor performance.
Entre...VENDORS SUPPORTING THE STANDARDS AND DOING IT RIGHT! ERDAS has really supported the OGC standards in an extremely MEANINGUL and HIGH PERFORMANCE manner. We are CITE certified OGC services and provide "under the hood" the depth and richness of format support, sensor model support, workflow and an out of the box end user experience in a single product that is expected of a commercial vendor.
If you really want to see the OGC services FLY on TERRABYTES worth of heterogenous data with real world use cases...the APOLLO Enterprise Suite is what your looking for.