Comment 12 for bug 259453

Pidgin does not follow an odd/even version scheme such as Gnome. Pidgin 2.5.0 is a major new stable version; they have not changed versioning schemes. Development is done using mtn, and the 'unstable' development has been conducted there for some time.

For further evidence that Pidgin 2.5.0 is stable:
Pidgin front page - http://pidgin.im/
Pidgin 2.5.0 milestone 100% complete - http://developer.pidgin.im/milestone/2.5.0
Pidgin at Wikipedia - http://en.wikipedia.org/wiki/Pidgin_(software)
Ask anyone at #pidgin on freenode.

I assume you've looked at the versions in current Ubuntu releases which is why you have raised your concerns; it is just coincidence that they have been even numbered releases in the past.