I think writing talent is less common, but not at all unheard of for verbally gifted children. I was similar to my DD in this way and won various writing contests as a child. To some extent, writing talent can be tied to a gift for imitation.

Going back to DS--his other skills are definitely much stronger. His teacher seems to think his writing is very good. It may be that I am just totally warped by DD. I find it a little concerning that he is still inconsistent with capitalization. He does use periods all the time now. Commas are inconsistent. His spelling has improved. I guess the strength of this bit is that it makes sense.