The difference between the treatment of Bellamy and Tevez is a reflection of a fact of life that's applied everywhere I've ever worked. If you p!ss off the boss but they rate you and want to keep you, then you'll get away with stuff; if you're someone they're happy to let go, the exit is usually pretty unceremonious.
The idea of taking Bellers aside and telling him he wasn't in the 25 several weeks ago, as suggested above, is nice in theory. I suspect, though, that Balotelli was earmarked as the replacement and they didn't want to shift Bellamy until the new player's arrival was certain. In other words, a degree of pragmatism was at play, which again isn't the best way to treat an employee but again it's totally typical in my experience for employers to put their own self-interest first.
The whole tread now seems to have descended into a blame game. Some slate the club, some slate the players. There's no doubt that there's fault on both sides, and while we can argue over where the majority of it lies, it seems rather futile to do so.
Having been undermined by the world being allowed to believe he was probably only here on a short-term gig, Mancini had problems with certain players that made it likely that he'd want rid of some of them this summer. In other circumstances, he may have been happy for them to be squad members this season, but I don't blame him for wanting to wash his hands of some of them. If I knew I could recruit quality replacements, I wouldn't want to build bridges with someone who'd said about me what Ned said about him on Soccer AM or who'd done what Bellamy has.
Unfortunately, especially if you're working under the pressure Mancini is, you need to be able to trust the people who work for you, and if they make clear that they think you're a c**t (as those two players have), that's very difficult indeed to do. As I said, you take a more pragmatic attitude with Carlos as he's much harder to replace.
Ultimately, both the manager and players are suffering because of the way Mancini's appointment was originally handled. I suspect players who disliked him felt emboldened to make it clear (I exclude Onuoha here - didn't his interview come after Bob was evidently staying) because they expected him not to stay, and maybe even thought they could make even more sure that he wouldn't.
The other point is that Mancini inherited a squad that had been assembled by a manager from a completely different football culture with a view to playing in a particular way. Having backed him very solidly in allowing him to recruit players intended to fit that style of play, they then bring in Mancini, who has a completely different way of preparing for and setting his team up for games. There were bound to be problems arising from this, especially mid-season and with Mancini allowed to make minimal acquisitions in the January window.
So all in all, if people want to blame someone, blame the club hierarchy for the backing of Hughes, then the abrupt reversal of policy. That's made an extremely difficult situation unavoidable this summer. There's room to criticise players, the manager and the CEO/Football Administrator for certain ill-advised actions, but the seeds were sown a fair while before this summer. All we can hope is that it's resolved as quickly and painlessly as possible. But I wouldn't be overly hopeful of that.
If anything positive emerges, it would be that the powers that be at the club might learn from an unhappy episode. And the criticism that's bound to follow, hopefully, will be used by the manager and his staff to galvanise the players who do remain.