check ou the last item on this link: http://support.apple.com/kb/HT4861?viewlocale=en_US
In my oppinin apple made a mess with reminders/alerts names and behavior. Things could be easier.
Anyway, apple regards the outlook message as a falase positive and states that oulook will still give us the alerts. I just installed iClound on outlook, so I don't know if that is true. Anyway, even if alerts are kept, two things are very annoying: 1) alerts are set to none by default when creating a caledar event in the icloud calendar from outlook (I used to use the 15min default on other calendars). This means that everytime I want a reminder for a calendar event, I have to remember to go and set it. 2) Having this idiotic message pop up everytime I create an event with a reminder will be a pain.
I'm going to try to stick to iCloud for now, but if this things start to annoy me too much, I'll just go back to using google calendar sync on all my PC's with outlook and google ical dav on all my apple devices and macs.
Hope Apple fixes this and improves icloud soon.