I don't think there is anything unique about experience in a game, he isn't the only legend Real Madrid has ever produced and they all have retired in peace, they have found something better off football that fetch them money but as for Modric, I think he wanted to stay by all means and Perez gave him a chance by signing a year contract and they maybe doing that probably they don't have the best man yet for his replacement, somebody young and talented.
If experience help players, I'm not sure Ronaldo would lose that penalty that in their Knockout stage for Portugal, he weep his eyes all through he match and was pet by his team mate not to cry, this is happening because Ronaldo is old, he can't be like his prime anymore, anything his doing now is just struggle to fit into a place where he is not supposed to be for that time. I hope Modric don't disappoint the team like that too in the end.
Coming back to modric, I still feel he makes some great impact in big games as an experience player IMO
Penalties have nothing to do with skills or anything other than luck. There is a bit of experience, feeling, just like gambling, even big players lose money!
For Cristiano Ronaldo I find his way to apologise from Portugal fans as the trigger that made media more interested in talking about it, otherwise it is just a normal thing like Messi, Benzema and basically every player that missed a clear goal or a penalty. It happens!