The problem with including Sallah, Willie, or Short Round in the wedding scene is that it would've made Indy's universe suddenly appear very small. It would be different if any of them had been in all three of the original films- regardless of the story's locale.
For example, if we'd seen Sallah in Peru, Cairo, India, and later Iskenderun...then, yeah, he's probably someone you'd expect to get an invite to the wedding. Otherwise, he's just a good friend that you expect Indy to visit in a certain part of the world.