Warwick has always had the capacity to solo Baron Nashor significantly sooner than most champions - Udyr is also relatively notorious for being able to pull similar things. Being able to do something pre-season 1 junglers were valued for doesn't change the fact it's not something season 3 junglers are valued for though.
Having a potentially end-game build of 2 and a half major items with boots makes that significantly less impressive. Especially a build that causes bonus damage to jungle monsters, bonus damage based on HP, and life steal.
You can solo Baron with any champion - it mostly comes down to lots of life steal or spell vampirisim. And you could probably solo him with most junglers at level 14 if you managed to grab the items listed.