A professional can use a calculator to perform division, but that doesn't mean that they shouldn't be taught how to do long-division by hand still.
A rocket scientist building a solid-oxygen booster hasn't wasted his time if he first practiced on model rockets and soda bulbs -- it may in fact have been a key stepping stone to getting where they are now.
In your professional career you might not use SDL, but that doesn't mean it's a waste of time to practice with it in the meantime. SDL greatly simplifies a lot of the complex and boring parts of multimedia work so that you can initially focus on programming interesting and useful apps. Once you're comfortable programming simple SDL games, and feel like exploring, then push it aside and try and make similar games without it, for the challenge.
Also, SDL can be used in conjunction with OpenGL, so if you feel like learning OpenGL soon, then the transition can be extremely smooth - you can actually be using both at once.
Think of it like a learners bike -- you don't get a 2000cc motorbike straight after getting your license, or you'll end up frustrated and hurt Much better off getting something simpler and easier to control until you're comfortable with it.
In fact, a truly seasoned professional programmer will be expected to be able to be given a new API, like SDL, and learn and start working with it in just one day. So practicing on many, many different APIs (and practicing the process of learning how to use new tools) is extremely important. As a professional, you'll need to be able to learn absolutely foreign tools, which you may only use once and never again, all the time.
Edited by Hodgman, 30 March 2013 - 06:51 AM.