The question of whether to use a traditional publishing house or one of the many self-publishing options currently available is fuel for an ongoing, though relatively new, debate. Each has the desired outcome for the author of a published book, and yet each brings with it a unique set of circumstances that are neither good nor bad. Many authors have come to rely upon both methods with good results. Though there is a niche being carved out in the form of Author Services Companies that may be difficult to ignore in the future, there will always be a demand for traditional publishing houses.
One of the main reasons for this remains the incredible amount of work that must go into the publication of any book of any length or subject. More than just the writing of the manuscript, an author must learn about information that is not necessarily common knowledge to most writers. Hiring or finding a graphic artist for your cover design and artwork, typesetting PDF's properly, working with editors, proofreaders, and publicists, creating e-books, and the myriad of details involved in learning about the various software used in the self-publishing industry.
On the Industrial or Traditional Publishing road, you're still at the same level as the fledgling self-publisher. Though you may have an arsenal of people who will take care of many of the details, you still need to be able to write a compelling query letter, a spectacular synopsis of your work, be able to format and submit your manuscript properly (which can and does change according to the publisher's guidelines), and find someone who is willing to read your book. Even after you've secured a manager, you will need to monitor their progress consistently and give them nudges when necessary (without pissing them off). You'll need to learn about the legalities of contracts and publicity, and once you do have a book deal, you'll need to communicate with all of their people too.
Much like any other career, networking and professional relationships are one of the keys to success. The relationships you must maintain and build are the same whether you use a publishing house or go the self-publishing road.
For most writers the choice seems to be a little of both. If you can garner a book deal with a publishing house, of course you're going to want to snap that up, but don't completely ignore the self-publishing process without at least seeing what it has to offer.