Lavabit didn't actually have the information in a format that was readable. In order to get it, they needed to change the way their system operated to decrypt the information the next time a particular user logged in. If one can force a person to modify the source code running on his servers, why can't one force a person to modify a binary distributed to clients?

From reading the arguments in this case, it's not clear to me that the judges would have been impressed by that distinction. Their focus was on whether Lavabit had the technical capability to provide the information the government demanded. In both cases, the answer is yes. We won't know the actual answer until this has been litigated. If it has and I've missed it, I'd love to see the case in question.