Behind the scenes, many Web sites are powered by Web-based content management software applications (A.K.A. "CMS" to those who like acronyms). CMS solutions come in many forms - they can be purchased off-the-shelf or built, licensed and customized to your needs by a Web development firm.
The benefit of having CMS is that you control your Web site's content - and you don't need to dial up a Web designer with expensive hourly rates every time you need minor information changed.
The challenge is that CMS solutions can be expensive for a small business to take on, and difficult to justify during the start-up phase. A solid, bare-bones CMS built-out can start at $2,500 and go on up from there, and that's just for the cost of development. This is why I've started recommending inexpensive (or free) blog software build-outs like WordPress to smaller clients (or even larger clients with tight budgets).
WordPress is blogging software, but can also be utilized as an extremely powerful - and customizable - content management tool. I'm seeing more and more websites being 100% built on WordPress platforms. As companies roll out blogging efforts in addition to their main, informational websites, my prediction is that eventually we'll see them consolidated into one digital presence.
If you're a large organization in need of a highly customized Web application and e-commerce solution, you'll definitely require some high-end development and/or CMS build-out. But if you're a start-up or a small business, consider using blog software to power your site, and save yourself a few thousand bucks.