I have been learning web design for a couple of years now. Up until recently, though, I never really understood how important specialization is. For the last few months, I have been moving from one language to another, learning bits and pieces. As a result, I have a pretty basic knowledge of many different web technologies.
Then, it hit me. Why would I only learn enough to get by on each subject? Why not learn as much in a particular area as I possibly can? That's my view now. I would rather be an expert in a single area than know a little bit about a lot of them. For me, the obvious choice of specialization is web standards. HTML was what first got me interested in web design, and I have always enjoyed writing HTML and CSS far more than something like PHP or ActionScript.
Don't get me wrong, though. I'm definitely glad that I have at least a basic understanding of programming and server-side scripting. I'm sure I'll have use for those things at some point, but I'm not planning on actively pursuing them at this time. Instead, I want to learn as much about web standards as I can. I kind of see it this way: I've been spending the last 22 years of my life learning and using English. If I had decided after two years to start learning the basics of Spanish, and then moved on to French a couple of months later and so on, what good would that be? Unless I'm some sort of genius (which I'm obviously not) I would have very elementary understandings of all of those languages. Likewise, If I devoted all of my spare time to learning more about the English language, I would greatly improve my knowledge in that regard. The same idea can be applied to web design.
I also think that specializing in a given area really makes you more marketable. Having enough knowledge of something to be considered an expert is a great bonus.
The decision for me to focus on web standards ultimately came down to whether I want to be a developer or a designer. When it comes down to it, I really like the front end of the web. Also, I tend to get really frustrated when programming.
Another major tipping point for me was Flash. At one point, I really loved using Flash. I used it to some extent in all of my projects. Then, accessibility became more important to me (also I got tired of the huge headaches I got when trying to program). In addition to not showing on mobile browsers, content in Flash elements isn't read through screen readers, and large Flash elements really increase load times. There are definitely appropriate times for Flash, though. Video presentation using Flash is great, for example. For now, though, I'm giving Flash a break.
Using web standards is a great way to ensure that your content is displayed on the vast majority of browsers. It also allows you to create more accessible, usable sites. This really appeals to me and further aided me in my decision.