Natasha is not a public person and there aren't many people to mourn her, aside from the Avengers, Yelena & co, etc. Vision's an android, regardless of the way he is perceived, he's body was recovered by S.W.O.R.D., not really much to make a service for. And Wanda is the only person who was actually close to Vision, more than on teammate basis. I just can't really imagine a big, flashy mourning for those two. There was also a tribute to Natasha on the AvengerCon.
