I believe exes are exes for a reason!
Having said that I understand it's "the in thing" for people to remain "friends" with their exes.
I suppose if they exchange emails from time to time or call one other a couple of times a year that wouldn't be a big deal.
However if they are talking to each other several times a week, exchanging birthday cards and presents....etc I'd feel like they are "emotionally" still connected. I'd also wonder if they would havee a problem with me doing the same thing.
If your heart and soul is into your relationship generally speaking you have very little interest in maintaining a relationship with your past. You can't get to 2nd base if you keep one foot on 1st base.
Needless to say if they have been in each other's lives for 11 years odds are they would just take their friendship "underground" if you were to make any demands or you mate simply tell you up front their ex will "always be a part of my life". Your options are to accept it or move on to find someone who feels the same way you do with regard to exes.