Technically your iMac came with that iLife software preloaded, it didn't come with the OS. If you had an older iMac and bought an upgrade for the OS then you'd have to buy the upgrades for iLife separately. (You almost always got a game too, again that wouldn't be there if you bought the OS itself).
What you say is true, but it's splitting hairs really. The fact is that unless actively deleted, every mac has video editing software installed from the day it was delivered. Still, I have to concede that although it is present, it was not actually shipped with the OS.
It's a pretty lame boast that has to be laden with so many caveats, though.
