As far as Gibson saying they use tight grain wood...that means (and hopefully they're being truthful) they are using naturally grown trees.

If you were to cut a tree down out in the forest and compare the rings to that of a tree that was grown in a nursery (lotsa chemicals to get them to grow fast) you'd see the rings are tighter on the natural tree.

Tighter grain = stronger, more healthy wood.

How does this affect the tone? I'm not sure, but I'm sure it affects it in one way or another. Hope this helps.