Depends also on what you mean by the "Standard Library".

Back in the day Ruby had built in language features (e.g. Innumerable), and a standard library that was bundled into the distribution (e.g. GServer).

More recent versions of ruby have significantly streamlined the standard library, pushing a lot of the functionality into Gems (libraries). Given that the use of a Gemfile to list library dependencies is absolutely standard practice, the upgrade path simply involves adding a line to the Gemfile.

In practice, these changes have been very well signposted before they have happened.