You could try Wikipedia: http://en.wikipedia.org/wiki/United_States_Bill_of_Rights#Ph...
Also consider that they Philadelphia Convention wasn't some magical aw-inspiring meeting of the minds as it is sometimes made out to be. Only 39 of 55 actually actually signed the constitution and several were so pissed off they just walked out. I'm sure lots of bargaining and negotiation was done and the 12 articles in the Bill of Rights was simply one of the bargaining chips.
http://en.wikipedia.org/wiki/Three-Fifths_Compromise
Committees are all about compromise and compromises are usually a worse solution in everyone's eyes. I'm not saying C14 threads are as bad as slavery, but they are a compromise that I'm sure no one will prefer to their native thread library.
I'm a bit surprise that ISO is even attempting to do generic threads. Who is this really a problem for? We have oodles of libraries that provide cross platform thread libraries. I don't see why we need the C standard to specify one.