All my cars have improved by quite a bit as they wore in.
My Jeep went from about 14MPG to about 18MPG (no fuel log from new).
My Fiat went from 30MPG in it's first tank to 50MPG currently (still not quite broken in mind you). Expressed in l/100km the first tanks where a dead on linear progression of 0.5l/100km per tank.
My Renault Kangoo went from 30-38MPG. The numbers on that one are a bit cloudy due to payloads, towing and so on. But if you exclude the tanks after I started towing with it, there's a nice gentle upward curve.
Renault Trafic returned 30MPG first tank, and has picked up about 0.8MPG per tank to 33MPG, only working on the 5th tank now.
I put these improvements mostly down to break in (eg as we all know rolling resistance improves as tyres wear - many have reported new tyres= bad MPG), as my Jeep improved all on it's own (pre hypermiler days) and the 20 MPG improvement on the Fiat
That car is also shared with a non-hypermiler so again suggest hardware improvements rather than software
I have fuel logs for three cars from new, they all improve over the first several tanks, infact, two are a near perfect linear progression. My used cars show no such trend, as if you can hypermile one car you can pretty much hypermile them all.