What I find mind boggling here is why anyone would stay. If you're not having a good time and I'm DMing, why are you staying? Is it some sort of sense of obligation to the DM? For me, if you're not having fun at my table, I'd much, much rather you went and did something more fun. You owe me absolutely nothing. I am offering a game. If you aren't enjoying it, please, by all means, go do something more fun. If for some reason I've removed a character from play for an extended period of time, I'd probably tell the player flat out and offer to let the player go.
It's baffling to me that anyone would ever have any problems with a player who wasn't having a good time, politely excusing themselves and going off to do something else.
---------------- Edit to add a thought.
[MENTION=6688277]Sadras[/MENTION], you've repeatedly made a distinction between the notion that this is a playstyle thing and bad DMing.
To me, any DM who would sideline a player for an extended period of time (say 2 hours, although, to be honest, even 1 is probably pushing it) and then get expect that player to stay at the session and actually get angry or hurt or offended that the player politely bows out and goes off to do something else, is a bad DM.
That someone would choose to stay is perfectly fine. But, leaving is also perfectly fine. The fact that a DM would get offended to the point of possibly consider booting the player from the group (which was at least one of the reactions from the other thread) is a DM I never, ever want to sit at a table with. Anyone who takes their game that seriously is someone I will not enjoy playing with.