Firstly, you're getting new tyres, new battery, new plugs, new brake pads, etc. The effective value of all that is probably around $1000 if you assume that these would all be half worn on a second hand car.
Secondly you're getting free roadside assistance. Five years of AA subs would set you back at least $500.
You're also getting a three or even five year warranty. How much does it cost you to buy mechanical insurance on your used car? $1500 or thereabouts?
A new car might potentially also give you less frequent warrant of fitness checks (depending on the outcome of the WOF review), free servicing as a sweetener in some cases, or the longer service intervals and better fuel economy that goes along with the latest engine designs.
I'm not saying that this makes up for the difference in depreciation costs between a new and used car, but the difference certainly isn't as great as some people think when you look at all the factors, and consider that new cars are cheaper than they've ever been.
I agree that buying second hand makes better economic sense if you're going to keep the vehicle for less than three years, but once you start approaching five years of ownership the depreciation averages out to a far more acceptable level.