char vs cl_char in API Calls

All OpenCl API functions use the cl_types with their fixed bit-sizes instead of the native c ones whose bit-sizes are not fixed, except for char and uchar. E.g. clGetPlatformInfo.

cl_char and cl_uchar are listed on page 157 of the specification.
Can this be changed so only cl_char and cl_uchar are used, or is there a reason for this?

Also there is nothing stated about the character encoding.