That's the official article from steelers.com that we've all read by now Im sure but let's think about this for a minute. It was eluded too in Joey's official release thread and we all know Koopa blames Colbert because he's all up in Tomlin's jock
Seriously though, this can very well be more of a power move by Tomlin to lay down the law early with this team, let them know nobody is safe, it doesn't matter who you are. Sure Porter was controversial, that much is clear but the guy made plays, was a leader, and dedicated teammate to the end who always had the back of his fellow black n gold players.
It's not uncommon for a new coach to come in, especially one who's not well known and doesn't have any HC experience to step up early and make a move to signify that's he's here and in charge whether we as fans like it or not. If Tomlin really wanted Joey and felt like he was a vital part of this teams success in his (Tomlins') eyes, then it doesn't matter what the cap says, Joey would still be here and he'd have gotten his bonus or a new contract by now. The fact is that Colbert is calling this a cap move, which it may very well be to some extent, but IMO this is more of Tomlin asserting himself and trying to head off any controversy before it starts, in his new regime.