From their introduction (or rather, from the backstory that trickled out from uncertain sources after the first Star Wars movies) Wookiees were designated as arboreal creatures. Judging from their appearance, I would equate them to any other large, tree-dwelling primate. They have opposable thumbs, long, gangly arms and legs and perhaps even opposable toes (we never do get a great look at Chewie's feet). I had no problem believing that they were capable climbers.
And then came the Zahn novels (Heir to the Empire). Now, overall, I liked these books, but like many creative folks, Zahn had to put his own spin on things. And so, when the Character's paid a visit to Kashyyyk (the Wookiee homeworld) there was a whole scene involving tree climbing. And wouldn't you know it, but Chewie and all his pals suddenly sprouted these HUGE retractable claws so that they could climb. At first, I was somewhat indifferent. Okay, I thought, so they have claws. Guess we just never dealt with that in the movies. I could buy into it. But then came the whole convoluted reasoning behind WHY we'd never seen Wookiee claws before—it was 'dishonorable' for Wookiee's to use these claws in combat for....whatever reason. I think it was something like "It lowered them to the level of a beast". That just sounded stupid. Both from a gaming standpoint and a logic standpoint. I mean, Chewie had no problems with going berserk, and in the game, that was a Wookiee 'special ability'. So flying into a mindless rage was fine, but using claws was a no-no. WTF?
In any case, Wookiee claws are just another example of something that didn't need explaining suddenly getting an explanation that was stupid (midicholrians are the prime example of this). I am peeved and I officially reject this 'reality' and substitute my own.