You put your finger where it hurts the most :-)

But there is hope...

Here are a few things to consider:

• The big players of today might not be the big players of tomorrow. They know that and you cannot win a market by holding information hostage. This is true not just for health, see what happened to Office file formats :-)
• Customers are demanding for more and more interoperable systems. Data and information needs to flow seamlessly across the continuum of care to enable better outcomes and business results. As an example see what is happening in the US with CCHIT, the certification authority for health IT: today they are testing functional specification but moving into the area of interoperability and support for select scenarios (the ones selected by AHIC and detailed by HITSP).
• Standards are (somehow) maturing in this area. Although we still have long ways to go, we are seeing a more concerted approach to information sharing based on use case scenarios rather than mere point to point interaction
• Moving towards SOA and more "composable systems". The whole software+services is not just a fad. Identity management services that today are local to your application or limited to the enterprise could tomorrow be a service in the cloud. That can easily be extended to terminology services, clinical guidelines and pathways, storage and so on. Who gets this in an industry that is 10 years behind in technology adoption?

Don't give up :-) if customers see value in what you're providing they will ask their vendors to open up. The pressure is building up and the market is ripe for change.