You're absolutely right, it wasn't always the case in the past the iPhoto would attempt to suck in all your video clips either. What happened I think around iLife '08 was they wanted people with still photo cameras that could also shoot video to be able to empty their cameras of EVERYTHING they might have on the camera whether or not it was video or still pictures. The side effect of that is iPhoto just assumes it supposed to manage everything on your behalf. But in fact in your case and in others you really want iMovie doing all the work.
I read up a little more on this and found out you can also drag the clips from the iPhoto Videos folder into other Events in the Event Library. So there's another way to do the moving of videos and it might be more straight forward than the complicated scheme I came up with previously. Here's what I'm thinking of:
1. Create a new empty event in the Event Library (File > New Event) Give it a name describing what clips will be going into it.
2. Go to the iPhoto Vidoes folder in the Event Library. Hold down the Apple key and start clicking once on each clip you want to copy to the new Event within iMovie. Once you have a good number (maybe 10-12) drag them to the new empty Event you created in the previous step.
This will NOT delete the originals, but merely copy them. Once they are safely copied into Event Folders using iMovie, you know they are safely there for you to use.
Downside to doing this is even though you have a copy, you haven't deleted the original videos sitting in iPhoto. So the second step in this process is to delete the videos in iPhoto once you have made copies of them. It's going to be tedious to do the book keeping to know what's been copied over and what hasn't. But you could also just do 'Select All' when you are in the iPhoto Videos folder (and that means it would select everyone in one shot) then drag all of that into the Events folder you created at the beginning. That would ensure everything got copied at least once into iMovie and that you still have the duplicate or back up vidoes sitting in iPhoto which can be deleted at a later time. What you choose depends on which is easier for you to manage. I think Select All is probably easier, but you might want to split things into new events as you copy them from the iPhoto Videos folder in the Event Library.
And again, do what you think is best I just wanted to include this as a smaller number of steps alternative to my original advice. Good Luck and may the Geniuses be with you.