Well, C4 is a completely different approach. And actually a very good one if it really works without restrictions.
But Unity is different. They just use CG and you have to code shaders and their fallbacks the same as in gamestudio. The only difference which is quite nice, is that you can link to another shader for the fallback, so that different effects can share the same fallback without the programmer having to copy and paste the code. This results in more shaders, that include fallback, which is nice but doesn´t really make a big difference to gamestudio.
There are probably a few more differences, but they should all be small... At least I forgot them, after writing a shader in Unity a few weeks ago .