My experience training with strikes in aikido is that more advanced practitioners demand serious attacks. There is an understanding that if you get punched, it's your own fault.
In my own experience (which may be different than yours), these serious attacks merely mean faster and stronger attacks which usually ends up like a traditional Japanese style attack, one hit, one kill sort of attack. That covers one sort of attacker in real life.
But many guys when they come at you, may throw a flurry of smaller punches which many Aikidoka are not necessarily ready to defend against. We might defend the first and even the 2nd but especially when real life punches aren't through a predetermined pattern, we usually end up getting punched.
Also I find that traditional Aikido uke attacks tend to have a big telegraphed movements that informs the nage what is coming. Again this may or may not be true in your experience but it's the general feeling I got from the dojos I've been to during my years of training. UK, Japan, Singapore, Malaysia and I think almost all of them gave me this feeling. Also, I find that these attacks aren't really spontaneous....
I would very much like to hear any Aikidoka who has experienced a dojo with true jiyu (or at least in my opinion what jiyu should be like) where the guy can come with ANY attack and even throw combinations not just the traditional Aikido ones. If anyone could share their experience with this and how it has helped their Aikido training (or otherwise), I would be very interested to know your insights on the matter.