It's been forever since I read Takei's book, or Shatner's first two...and if the others wrote a book, I didn't read them. BUT...arn't the most damning accusations that Shatner would ask for "their" lines to be cut or given to him? Or that he would say things like, "We don't need to cut away to Sulu here"...and finally if Shatner DID intentionally flub those lines to keep Sulu from being promoted?*
It's things like that, that would seperate him from Nimoy. NOW...did they have to make a living off it? Did Doohan have to make it a blood feud? No. But I'm just pointing out why Nimoy might escape scrutiny.
*Why Shatner would do that, and why Takei would care so much about a fictional promotion, I have no idea.
edit: I would also point out that I don't have a 'side' here. If anything, I find it curious that it took forever for Doohan to bury the hatchet with Bill. If Doohan was rebuffing Bill practically up to Doohan's deathbed...well...all props to Shatner for trying to make amends LONG after I would have given up.