The 'ink' (it's really toner) cartridges that come in new printers have a fraction of the levels in them as retail cartridges. They're referred to as 'starter kits' if you look in the small print. You're looking at a false comparison there.
The HP laser printer I bought recently, on the other hand, did come with starter cartridges with a smaller amount of toner. My impression is that starter cartridges are more common with toner than ink.