I ran in to a situation this week whereby if you don't pay for the Milestone Corporate edition you can't "Lock or Tag" video from deletion unless you are on their Corporate edition software. This feature is called Evidence Locker. Now Evidence Locker has some cool features but if I just need to keep some video from being deleted for a couple of weeks while an investigation is going on then you really shouldn't have to pay an arm and a leg for something as simple as this. Also you can't even add this feature as an option to any of the other models.
So in the comments shout out other brands that do allow this as part of the base system. Either a simple appliance or all the way up to an enterprise type system.