Well, don't forget that the Kobayashi looks exactly like Harima Kenji (so Harima's a self-insert manga character who draws manga with a self-insert character.) And his wife is half (like Eri,) from what I've heard in previous SR threads. Of course, from what I've also heard his wife also used to be his assistant (like Yakumo.) And of course therefore it's possible that there's just as much of his wife in Tenma as well, smokescreening it further.
Meh, personally I think that just like all fandoms people will root for the character they like most to get the guy/girl they want, or maybe for the character they like least to *not* get what they want. ie people who like Eri more want HarimaxEri, people who like Yakumo more want YakumoxHarima, and they all hate anything that gets in the way of that, ie Tenma. It usually has very little to do with what coupling would actually work the best.
Personally I think HarimaxTenma would work out very well if Harima could just stop being so nervous around her and worrying about CONFESSING HIS LOVE and just talk to her like any other person. I mean, they're practically male and female versions of each other, at least in the fact that they're both idiots, so they could probably hit it off fairly well if they had a chance to. Whether or not that would work for or against them in a romantic relationship, I don't know.
If they ever intend on taking HarimaxTenma all the way I'm calling it right here that she'll find out about Harima's feelings when Tenma misunderstands something Harima does and decides that he's actually a horrible person after all for the 984th time and Yakumo finally snaps and screams "CAN'T YOU SEE HE LOVES YOU YOU STUPID BITCH?!?!?"