In my opinion, the Aikikai-style randori (as opposed to other kinds of randori) that's done in nearly all dojo do not mimic so-called "real life" situations at all. There are a boatload of "rules" that are imposed on both the attacker(s) and the defender.
If someone grabs my shoulders and stands there strongly, I can't break someone's nose? If someone charges at me like a bull, I can't just simply throw them right into the shomen? What about a sharp open-handed backhand to the eyes?
This kind of randori, I think, is basically an exercise (just like almost everything else in aikido) to get people to practice their movement -- tai sabaki. Too many people get caught up in throwing their uke rather than moving, and I feel that randori helps people in working on moving around...