Through the first six games, Jared Sullinger is averaging 3.3 three-points attempts per 36 minutes, while Kelly Olynyk is averaging 2.5.
For comparison, Bradley is at 2.7, Green at 3.0, Lee at 3.3, and Crawford at 3.8. Last season, Lee, Green, Bradley, and Barbosa were all in the 2,9-3.3 range, while Pierce and Terry were trying over five threes per 36 minutes.
I'd argue that these young bigs are taking threes, especially when wide open, because Brad Stevens wants them to and Stevens wants them to because Ainge wants them to.
If you are building around Rondo, one of the pieces you want is a stretch four whose three-point shooting compensates for Rondo's deficiency in that area. I believe that one of the primary goals of player development this season is to see if one of the young Celtics bigs can fit that role.
If neither proves to have potential in that area, look for at least one of them to become trade bait as Ainge continues looking for three-point shooting bigs who can be credible team defenders. I predict that people who think bigs should be glued to the post area are going to go through periods of hating this team (until Ainge's roster strategy leads to the next title).