Summary:
Can I program a \"thick client\" game in C without reinventing wheels, or should I just bite the bullet and use some libr
One consideration in favor of C/C++/obj-C is that you can mix and match various libraries for different areas of concern. In other words, you are not stuck with the implementation of a feature in a framework.
I use this approach in my games; using chipmunk for 2D physics, Lua as an embedded scripting language, and an openGL ES implementation from Apple. I write the glue to tie all of these together in a C language. The final product being the ability to define game objects, create instances of them, and handle events as they interact with each other in C functions exposed to Lua. This approach is used in many high performance games to much success.
I'm pretty sure most modern games are done in C++, not C. (Every gaming company I ever interviewed with asked C++ questions.)
Why not use C++ and existing libraries for physics + collisions, sound, graphics engine etc. You still write the game, but the mundane stuff is taken care of.