One thing that annoys me from the beginning of my work with MS Outlook is that I don't see who was invited when I receive an invitation. Outlook does not show this useful information by default just like HCL Notes for example. At this point (amongst many others) I really miss Notes...
Anyway, I have to use Outlook. I accidentally found the "solution": open the invitation (regardless if you already accepted it or not) and find the "Schedule Assistant" button in the ribbon (it's called "Terminplanung" in the German client). Click it and you see all persons and resources invited to this appointment.
At least there is a way to achieve this but honestly, Microsoft, why do I have to do that instead of just seeing all names in a simple row right on the default view?