I've never seen a game that needed to make room for more content before, Unreal Engine must be one ****ty engine if once you finish a game with it you have a limit of how much stuff you can add to it with updates before needing to delete stuff to make room...
It's a touch more complicated than that, yes the unreal 2.5 engine (that's a rather old engine now mind you) isn't the most stable, but still better than a lot of others.
Last year during the event TWI just added a load of new stuff on top and it caused a load of problems for peeps with machines just on the line of memory. And even some for those that good machines. So to avoid making content just to then loose chunks of regular loyal players and have to deal with the fall out they attempt to keep strict memory limits, hence why the xmas zeds are not as detailed as they once were and things like weapon stockpiling was striped out.
Edit, and yet they manage to keep adding new shiny toys in. And before you decry that the weapons will take up as much space. You are looking at ~100mb for a new voice. Where is a weapon is going to be about ~20mb. Much smaller hit for a lot more.