If players know my real name and use it, I consider it perfectly fine. It probably means we have been playing together a while and have built some sort of relationship, not just I added you on xbox, we are friends. I kinda even expect my friends I know outside of online gaming to use my real name. Plus using my real name probably grabs my attention a hair faster than my gamer tag anyway. You friend is just being that way because he can. No real reasoning behind it.