There is a very specific reason for this.
Audi lowered the 1st, 2nd, 3rd gear ratios for the DSG.
This has been done specifically to give an impressive 0-60 time.
The trouble comes when you hit 60mph, when 3rd changes to 4th.
There is a big gap, so it really struggles to pick up in 4th.
For proof, look at the 0-100 times.
The 140 may only take 8 or so seconds to 60, but it takes a whopping 26 seconds to reach 100.
That's 5-6 seconds slower than a standard 320D.