Comment 1 for bug 1310292

It appears upstream (Debian) Ruby package changed this during the Trusty freeze:

ruby-defaults (1:2.0.0.1~exp3) experimental; urgency=medium

  * ruby-all-dev: migrate from Ruby 1.9.1 and 2.0 to Ruby 2.0 and 2.1
  * ruby: remove Breaks/Conflicts/Replaces against old interpreter packages
    as this will force the removal of old interpreters from users' systems
    (Closes: #740733)
    .
    The following upgrade scenarios from wheezy were tested, still work fine,
    and leave the old interpreters alone:
    - ruby
    - ruby + ruby1.8
    - ruby + apt-listbugs
    - ruby + ruby1.8 + apt-listbugs
    - ruby1.8 + apt-listbugs

 -- Antonio Terceiro <email address hidden> Sat, 29 Mar 2014 16:12:05 -0300

Is it possible to integrate these changes into Ubuntu so that the package installation behaves as a user expects? I can't imagine anyone who wants "ruby2.0" would expect ruby 1.9.1/1.9.3-p484, especially as the default version.

Yes, update-alternatives is a thing, but this is an extra step which should not be necessary.