99% of the time the papers see the pictures on Facebook or Flickr etc and approach whoever uploaded them because they want to write an article about those images and how they came about. I can't speak for the stories given by other people on whether they are genuine but indeed the couple of times mine have been published certainly have been.
I work with a small local group of friends and how we go a out exploring is different to other groups around the country really, we do not break in, we do not take anything and we leave no trace - Only there for the pictures. I've read quotes from other explorers who go under well known usernames on urbex forums (I don't post on those forums any more having learnt what most of them are all about, just fronts for dodgy activities in most cases). It's all the politics side of things as mentioned before and it's just not worth it.
Speaking of which.. Believe it or not, getting urbex pictures published brings more hassle than bragging rights. In the cases where a certain well known urbex forum, if it's not one of them featuring in a media article then they will bandwagon together and spend days posting up threads about it and how the people who gave those pictures to the media are awful and ruining urbex for everyone else (that's just putting it nicely for this forum, can't use the language here some used over recent times
).
As for being a crime, under certain circumstances 'Trespass of the land' can be considered a crime (Criminal Justice and Public Order Act 1994) but it's up to the court to decide what to do about it if a claim is made. Nobody that I know of has been charged with any offence. Those that have been seen by the police on site have only been questioned and let go because there's been no evidence of a criminal offence being committed, simply people taking photographs and nothing more.