It's also a lot easier to release a new version of a package to fix a bug than do a bugfix release for the entire language toolchain, which is what would be nee

It's also a lot easier to release a new version of a package to fix a bug than do a bugfix release for the entire language toolchain, which is what would be needed in order to update the standard library. With Rust releasing a new minor version every six weeks, I think minimizing the chances of additional releases needed in between them is probably a good thing.