Ubuntu and what?
Ubuntu is an operating system, with a few general purpose programs thrown in. It isn't a suite of bespoke medical record management software. Installing it in all hospital computers will result in them becoming unusable, because they won't be able to run the packages the hospital is using.
That's the same problem I have with the various Linux offerings. They won't run my online poker client. I don't know any poker site that offers a Linux client, and if they did, would it work on Ubuntu, Red Hat, AND Suze? I have dozens of programs that I can't run on Ubuntu. I have a machine set up with it, but I seldom turn it on.
You might as well say that hospitals should run on Macs. Probably dodge the malware just as well, but they still couldn't use their computers for the programs they want to run.