It's really not, though. If you're in Epic, then yes, you're a big enough gorilla that most ancillary systems have to be able to export. But one of the real fails with "meaningful use" was that interoperability was not required until long after implementation, and the few standards that exist (HL7, ugh) are downright horrible. Even transferring information within a health system is often a nightmare, as each EHR has its own data structure. It's extremely frustrating when information is entered in a structured format at one entity, and then it has to be transferred as a text file, and at the other end you have to manually enter things back in a structured format.
It's an area that's ripe for a game changer however. There's just so much low-hanging fruit. For instance, when ordering a lab, on my side it prints out the associated codes, and a tube of blood is hand-labeled. The stack of printed orders and tubes of blood are then taken to the lab, where a technician matches the printed papers to tubes, then re-enters the patient data and testing codes at the EHR on their end. What would make immensely more sense would be for the codes to be sent electronically, with an identifying label printed out on my end. Same thing happens with imaging, with orders and codes printed out on my end, then the radiology department determines that you can't use that code with that order, and phone calls back and forth ensue. A smart system could determine the right code at the outset, which would be transmitted electronically. None of this usually happens because the systems won't talk to each other.
Dave