creative commons vs gfdl

Just out of curiosity, why is the wiki licensed under the Creative 
Commons? I'm sure there's a good reason, but it keeps us from using GFDL 
source material from the wikipedia, LDP, and a lot of man pages. I know 
that a lot of people are going to think that it's better to do 
everything from scratch, but not having to reinvent the wheel would save 
a lot of time.

On related notes:
Is it legal to relicense Creative Commons material under the GFDL?

If we do decide to migrate to GFDL, I would personally recommend keeping 
material created before the change over date available under the CC, 
since it's less restrictive.

What's the policy for combining a mature article with a less mature one? 
For example, merging two articles on the same subject but with slightly 
different names (or captilization)? The person who notices the 
duplication might not have enough time to completely merge the two 
articles seamlessly. Just cutting and pasting the smaller article onto 
the bigger article is ugly. And completely replacing the smaller article 
seems a bit preemptive - there might be information in the smaller 
article that the larger article lacks.