These questions are just "list of" questions. I don't doubt their value, but recent StackExchange philosophy seems to be to shun these kinds of question these days.
Pros of keeping them:
- they're common questions people have, and might drive traffic to the site
- shutting them down may seem overly moderator-heavy
Cons of keeping them:
- As with all external resources, there's the risk of them going away, not being maintained, etc.
- They are usually not very specific, so the variety (and quality) of answers is going to vary wildly
- Most "professional game developers" probably make their own art (or outsource it)
As always, the guideline of what kind of questions shouldn't be asked is found here: http://gamedev.stackexchange.com/faq#dontask