Well.. I know other GSDs that play with other dogs.. so I am going to say it's all based on the individual dog. So in this case, it's an Ace thing, and in my case it's a Titan thing. Titan could care less about other dogs. He MAY sniff them, but he really couldn't care less. The only time he interacts is when I puppy sit and even then, he doesn't want much to do with the other dogs. I watched 3 dogs a couple weeks ago and he would be outside watching them but not playing, even when "asked" by them to play. Then would just come inside with me.
I came to the conclusion, after reading a lot here, there is no need for him to LIKE other dogs. He only has to not be aggressive toward them (IMO) So we go to the dog park and other dog friendly establishments more so I can bring him with me places and we can play in a larger area.
EDIT: I will add that in out home, only, he doesn't tolerate rambunctious play very well unless he really knows the dog. Doesn't escalate anything, just makes them understand he isn't in a playful mood.
Commander Charly Titan (GSD)-15 Jan 2010