iMove '08 should have been called iClip 1.0. It clearly wasn't an upgrade from iMovie HD, it was a new product.
At the time I wrote:
Well, Apple didn't do the honorable thing for iMovie HD users, but the new Final Cut Express is out. Users of iMovie HD should probably forego the iLife 2008 update and buy FCE 4 instead.
...The honorable thing for Apple to have done would have been to provide iMovie HD users with an upgrade path to Final Cut Express (which might also require some updates to FCE, I'm not sure how serious Apple is about that product)...
I'd give them points if they were to provide a $100 upgrade path for users of iMovie HD, but I admit that would pretty hard to police. The new product is $200, so heavy users of iMovie HD will probably pay up.