I don't think it's entirely 'unrealistic', as you say. I think that some, not all, but some players would hold a grudge against a team for years. I don't know how it's being coded, if EVERY player didn't let you resign them for the remainder of their careers if you'd cut them, yes, that would be unrealistic. But if the occasional player says, 'screw you, you cut me and I'm not playing for you', I have no problem with that. I know that you probably want to sign whoever you want whenever you want, that's fine, I just don't have a problem with it.
I think that one of the issues with the game is that it's too easy to NOT give up good players. If you have a great team that's nice, but if you **** and want to get better it's tough when guys are resigning starting players for cheap. The contracts supposedly have been upgraded in the new release, and that's awesome. In the real world, it's hard for GM's to hold on to talent, it's been too easy here.