Not true. The latest version (SDL 1.3) is up to date. Check out the docs here. SDL 1.3 uses OpenGL for its rendering backend, supports multiple windows and so on.
I'd suggest not wasting any time on SDL. SDL is outdated, and lacking many features that SFML provides.
SDL has fewer high level features than SFML does (SDL does have addon libraries for some of these features though). For example SFML has image loading built in, but in SDL you would usually use something like SDL_image. SFML does provide a lot more rendering primitives than SDL does (eg, shaders) - SDL definitely aims to be lightweight and low level (eg a thin layer to handle windowing and input while you use OpenGL directly).
SDL has a C API instead of an object oriented C++ API like SFML has. SDL supports more platforms. SFML has networking support built in, SDL does not (but again, theres an addon library for it). SDL 1.3 documentation is still very much a work in progress though, while SFML has solid documentation. Besides that, they are more or less equal.
If you go with the old SDL 1.2, it has a lot of documentation available too and is rock solid, but you lose out on a lot of features like hardware accelerated rendering (unless you manually use OpenGL) and multiple windows.
Having said all that, I would suggest using SFML since it will get you started quicker. SDL would be a good choice for someone who already knows what they are doing and want a base to build a custom engine on top of, but SFML would be, IMHO, a better choice to get started quickly and learn game programming since it provides many more high level features, but these may get in the way if you are trying to build a truly custom engine (which, unless you're an expert, you shouldn't be doing anyway).