The common mantra is always "writers write," and less and less opportunities are available in paid spots right out of college (sorry, Rick Reilly's commencement speech). If the local paper's high school stringer beat is being manned by a 10-year vet, the kid might not have a chance to get his foot in the door.
Meanwhile, economic factors make mobility more difficult today as student loan debt means that young journo is probably living with his parents and paying off huge student loan debt and most entry level jobs don't pay enough to facilitate a move. This isn't meant as an all-encompassing/every situation description, but it works as a general swath of the industry.
So, in our global world, sometimes it makes more sense for certain people (myself included) to get their feet wet by writing about subjects they know, refine their craft, hone their voice, make a name for themselves, learn best practices, be put to the fire of public opinion (and gain that thick skin), be edited—hopefully well, take assignments, etc.
I wouldn't say that blogging *will* or *does* lead to other opportunities, but I know a dozen guys who did the ol' answering phones and writing down softball scores for a year or more without that leading to other opportunities either. For every 1,000 guys out there trying to make it, a handful will do so in any meaningful way and will probably each have a different route they took to get there.
