Many sensible replies on here but Genghis sums it up to perfection and I'd only like to add a footnote about the specialist press.
The specialist press needs people who know the industry and that often means retirees or just industry people who like to write and like the broader contact with the industry.
But those people (and their editors/publishers) often find themselves lacking in journalistic skills. They can write, yes, but it takes them twice as long or more to write an article; they see all sides of the issue in shades of grey and agonise over the details trying to be fair; they know so much about the industry that they let their personal opinions creep into the text; in journalistic terms they are inefficient and terrible on deadlines. And they tend to be more expensive than the young professional reporter.
Specialist publishers have to try to balance that inefficient expertise with the more productive "real" journalists and hope the experience will rub off on them. Tain't easy. "Experienced" ponders motives, mulls over scenarios and few things can be more irritating than a hack who's got 10,000 characters on five different issues to produce by 1700 TODAY and needs the text equivalent of five soundbytes. "Experienced" soon learns he'll be tarred by association with the "hack" brush. With few and honourable exceptions he will eventually either find greener pastures or assume the cloak.
If you're a potential source within the industry, my own suggestion is be cautious, as you would be in any contact with outsiders. Take your time and get to know (e.g. via Google) what sort of stuff the person who contacted you is writing, and try to understand what their agenda is. Handle it right and, as Genghis says, it's an excellent way to put your own ideas across or to boost your own company's image. Build up trust and you'll find information is very much a two-way street. And to hell with anyone whose primary concern is his/her deadline.