Perhaps "pseudo C" is the wrong description and the syntax is obviously derived from C and you can use C/C++ code inline as well. However an arduino sketch is still obviously a lot simpler than an equivalent C project that has to have far more explicit includes and definitions.
So for a test, pick any specific Arduino sketch example (for an atMega168) and show the exact equivalent with winavr gcc code.
As the other posters have said, The Arduino uses standard C syntax. It does add prototypes and includes to the main sketch file in its build process and if you look in the applet subdirectory of any a sketch you can see the content of the source files that are passed to the avr-gcc compiler.
The build process is described here: http://www.arduino.cc/en/Hacking/BuildProcess.