I personally don't believe that open source software will lead to the death of web development. Rather, I think it creates a prime opportunity for web developers to expand their skills.
Both "off-the-shelf" web software and custom-coded web projects both have their own purposes. Custom projects that are coded from scratch, or near scratch on a framework, are great for end products that are unique or require an extreme degree of customization. Web applications like Mint and Meebo are two good examples of this.
However, lots of the time, you're doing something simple, like a bunch of web pages or a blog. In this case, there's no reason to reinvent the wheel. By using an open-source off-the-shelf product, a lot of the basic components of such a project, like adding and managing posts, are implemented for you.
Personally, I've become a fan of the WordPress platform. It's a quick way to get a web project up on its feet, content can be easily changed later, and it allows for an impressive degree of customization. Seriously... if you're willing to dig in, you can pull off some pretty impressive stuff.
But you're not going to get any impressive results out of WordPress - or any other CMS - unless you've got some web development experience under your belt. I started off years ago in HTML, then moved my way through CSS, JavaScript, then PHP/MySQL. These are the tools that provide a proper footing in creating content for the web that you need to know before you can grow into more advanced development.
Now, marketing someone else's open-source product as your own and not providing proper attribution is pretty darn shady, and I'm pretty sure it's against the GPLs that most open-source projects release under.
Anyway, that's my two cents on the issue.