In C, at least, compared to the commented out version or removed (when using versionning) variant, the code is still present and builds (and will break upon API

In C, at least, compared to the commented out version or removed (when using versionning) variant, the code is still present and builds (and will break upon API change, guaranteeing it to be up-to-date), is present when re-factoring (not necessarily easy with all version control systems), and has no impact over performances (might not be true with PHP). So this can be seen as a feature, actually.