Another question came to my mind. Why do (or did?) Sakumoto seem cold to each other? I guess it's because of their personalities (duh!). I guess (OK, another guess. This post is gonna be written merely based on my guess) ... I guess Sho and Jun is the type who build "wall" around themselves and to be close with them other people have to break that wall. The other three has successfully break their wall. Ohno who freely and clearly showing his affection and saying stuff like "daisuki" and "aitakatta", Nino who will stand or sit really close to them, invading their personal space, Aiba who is ... Aiba, you know, Aiba with his tennen and kind personality. Ohno, Nino, and Aiba, can break Sho's and Jun's walls. However, Sho and Jun never break each other's walls. They're just not the type to break someone's wall, I guess (another guess!). Sho seems have lowered his wall. Jun? He lowered his wall on concert but still doesn't show affection in variety show. He's gradually following the other four on term of silliness tho.
For a group that has been together for almost 20 years, through thick and thin, I'm pretty sure they are closer than they seem. Well, many fans think so. However don't expect them to be playful like ohmiya and juntoshi in concert.
That's all my guess.