Please drop IRB's version in favour of Ruby version
It seems that IRB's upstream lives in Ruby's SVN. There is no way how to update IRB separate from Ruby. From that point of view, it would make sense to drop IRB's own version numbers in favour of Ruby versions instead. The IRB reports this version information:
However from the IRB changelog  it is clear that there went some changes in meantime, so the IRB's versioning is not reliable and does not make a sense IMO.