I don't think that's a general oipnion about what's being said on autobio. There are some kind quotes, yes, but for the most events between the two he blames Johnny. He literally wrote that it's all JM's fault that their relationship is broken. Morrissey wrote in the open letter as if he had always complimented Marr, but that's simply not the truth. Morrissey himself made digs at Marr sometimes in spoken interviews or at his concerts.
Where does he blame him? I can't think of much. He mentions a time where he writes to Johnny, they go for a drive and then M ends up shouting that he doesn't understand why the split happened - that's fair enough. There's a bit of schadenfreude when Johnny gets kicked out of the Pretenders. He's irritated by JM's comments in the media and has memorised all the offending headlines ('
Morrissey was hell to worth with, says Johnny Marr') - and he gets miffed with the courtroom performance. That's pretty reasonable stuff, isn't it? It's not cruel.
Most intriguing to me was that he doesn't explain why things faltered again after that pub meet in 2008 - he just says "Johnny tells me he is ready to reunite" and leaves it hanging. Whereas in JM's retelling of it, things were great for a few days after and then Morrissey went cold.
To me, their grievances look like this:
M - Johnny blames me for his leaving and has never forgiven me. He thinks I'm evil, slags me off and talks like he hated being in The Smiths
J - Morrissey blames me for leaving and has never forgiven me. He thinks I slag him off incessantly, he thinks I hate him, he blows hot and cold.
And on and on it goes. The split is like a tumour in their relationship, they just can't work it out.