Cummins have been using 14:1 compression ratios in their highway/off highway engines for decades; it's not a new thing.
Older pre-combustion chamber engines needed upwards of 23:1 compression ratio because of the massive heat losses in the combustion area, and in most cases required cold start assist (glow plugs, ether injection, inlet heating element etc) even in hot ambient conditions.
In terms of modern electronically controlled, direct injected, common rail/accumulator type engines, there are a few things that allow lower CR's. The aim (surprise, surprise) it is to do with emissions; NOx in particular.
Higher injection pressure (2000 bar) ~ no, allows the fuel to be atomised better than the older hydro-mechanical systems, but even the old Bosch PD system in the affor-mentioned golf had a peak injection pressure of over 1000bar. Higher injection pressure (and electronic control) allows better control over how much, when and how many times fuel can be injected into the combustion chamber in one cycle.
Turbos are better? More accessible to the mass market sure, but the majority of turbo chargers fitted to the garden variety passenger car still have conventional bush type bearing systems, waste gates and the same combination of materials used since day dot. Variable geometry systems - absolutely the best thing ever combined with turbos, especially for low capacity, high speed C.I engines.
As mentioned, the derived CR is basically what is needed to get the in-cylinder temp to around 450deg C to allow auto-ignition when fuel is added. The figure I have in my head is around 20bar +/-2 to get that temp. Most modern common rail c.i engine don't need glow plugs to aid starting - they're there to reduce knock during warm up, and of course emissions!
