TCP/IP is so well defined because the engineers on these small teams are the ones publishing the standards. It isn't like they are simply reading a spec out of an existing document and coding up a conformant program.
Err, yes - that’s what 98% of modern TCP/IP development work is. There aren’t frequent new RFCs for TCP - it is established, standardized, and stable.
Non-technical stuff is crazy complex compared to purely technical stuff, which tends to be a lot better defined.