No, it shouldn't be the copyright owners responsibility. Thats like saying "Well the door was unlocked so I took the TV". That's still stealing the TV.
Google can be stopped by robots.txt, hotlinkers can not.
As for being able to protect against hotlinkers, some file types are easy to protect, as long as everyone would show their referrer. It's becoming more and more common for people to disable that, either knowingly or (often) unknowingly. Many firewalls disable it and never mention it to the user. As far as I remember other filetypes (video and audio) are more difficult to protect without annoying visitors (requiring registration etc.). Content creators spend too much time as it is protecting what is rightfully theirs, and get precious little time creating new content.
Reading that article I have to say I'm on the side of the judge 100%, Davis hotlinked a file and got caught. I see no reason for him to not link to the page the file was on. I'm also very much questioning the reporting sites motives. Even calling it deeplinking is a very different thing than what happened. (Perhaps the wording is used differently in th UK?)
I'm all for deeplinking (linking to inner pages) I encourage it on all my sites. Hotlinking (linking to media files) however is theft, plain and simple.