If 1.year = 365.25.days, then 1.month should be equal to 30.4375.days

These are convenience methods. The API docs explain how the should be used:

  # These methods use Time#advance for precise date calculations when using from_now, ago, etc. 
  # as well as adding or subtracting their results from a Time object. For example:
  #
  #   # equivalent to Time.now.advance(:months => 1)
  #   1.month.from_now

And also how not to use them:

  # While these methods provide precise calculation when used as in the examples above, care
  # should be taken to note that this is not true if the result of `months', `years', etc is
  # converted before use:
  #
  #   # equivalent to 30.days.to_i.from_now
  #   1.month.to_i.from_now

And also suggest what to use for precision arithmetic:

  # In such cases, Ruby's core
  # Date[http://stdlib.rubyonrails.org/libdoc/date/rdoc/index.html] and
  # Time[http://stdlib.rubyonrails.org/libdoc/time/rdoc/index.html] should be used for precision
  # date and time arithmetic

Most importantly they behave as expected. :)

If you can provide a good reason as to why this change needs to be done I'll reopen the ticket.