The summary of the python3 package is currently:

             Python 3 is a new version of the language that is incompatible with the 2.x
             line of releases. The language is mostly the same, but many details, especially
             how built-in objects like dictionaries and strings work, have changed
             considerably, and a lot of deprecated features have finally been removed.

And for Python 2:

              Python is an interpreted, interactive, object-oriented programming
              language often compared to Tcl, Perl, Scheme or Java. Python includes
              modules, classes, exceptions, very high level dynamic data types and
              dynamic typing. Python supports interfaces to many system calls and
              libraries, as well as to various windowing systems (X11, Motif, Tk,
              Mac and MFC).
              
              Programmers can write new built-in modules for Python in C or C++.
              Python can be used as an extension language for applications that need
              a programmable interface.
              
              Note that documentation for Python is provided in the python-docs
              package.
              
              This package provides the "python" executable; most of the actual
              implementation is within the "python-libs" package.

Since Python 3 is the default Python now, it should be the other way around: python3 should define what it is, and python2 should say that it's an older version.