Having done multi system projects you are spot on. Even those libs that cover over some of the differences tend to have a lot of interesting edge cases. For e

Having done multi system projects you are spot on. Even those libs that cover over some of the differences tend to have a lot of interesting edge cases. For example threading will act one way on windows and a subtly different way on linux if you happen to use one of the popular threading libs. Even the CRT can have different cases for something simple like 'printf' (always re-read the docs for your compiler and platform before you port). So you end up with this weird glue abstraction layer anyway and quickly end up with config files for your paths.