I don't see how it follows that you can't have a functional language controlling an x-ray machine. You can make an appeal to complexity, I suppose, but this can be managed. If Erlang is used to create a 99.999999999% reliable cellphone infrastructure (http://stackoverflow.com/questions/8426897/erlangs-99-999999...), I believe it can handle medical device functions :P I mean seriously, at that level of reliability, even if you have a health-critical device with literally just 10 assembly instructions, a cosmic ray could still flip a bit (http://status.aws.amazon.com/s3-20080720.html) and cause a catastrophe!
And as far as Java (which I'm not necessarily a fan of, I'm just making a counterargument) and medical devices, look here: http://www.oracle.com/us/technologies/embedded/embedded-java...