People have got in trouble doing cranes before as mentioned, and no doubt this does set a precedent by which others could be prosecuted in a similar way. Looks like they didn't actually get caught doing it though?
My two cents is that they were successfully prosecuted because: A. They were actively endangering their own lives and those of others, and B. they stuck videos of it all over the web, which garnered both the attention they wanted (possibly) and that they didn't (clearly).
I don't think I actively climb cranes in my city, certainly not as a specific target. I've done a fair few over the years and seen Cardiff from a whole bunch of angles and the process itself becomes very repetitive (just a personal opinion I know), but it seems the practice itself has become a whole sub-practice where once it was just something most of us did for fun when visiting mates in a different city or something, and this itself is hard not to relate to the whole 'buzzfeed viral rooftoppers go to [insert megalopolis name here] and smash it all over youtube and facebook' thing. I just share here (occasionally) and privately with mates or on facebook, where you have to be my friend to see my posts. I'm not really too worried that this will ruin anything!