Bandwidth isn't the primary concern here. CPU time spent parsing/unparsing is. Depending on how your application is structured, it can actually dominate time spent in application logic. Whatever the case, it's simply waste heat being added to the universe. Use a little-endian, 64-bit-aligned binary format, and parsing overhead simply goes away.

Great point. I'm not one to over optimize, but seems like parsing messages for internet sized apps is worth spending a little effort to save energy and environment.

Please elaborate on the ways in which protocol buffers conforms to the definition of the word "proprietary".

Unless you are communicating C++ services for example and you prefer a lib that does the parsing and transformation to native object for you