First, you can see the musical scores in question...here is the musical score of Mozart's cadenza (the one Abbado preferred) [pdf]
The one Hélène preferred, by Busoni [pdf]
An alternate cadenza by Muller [pdf]
Next, take a listen to the passages in question with host John Clare [mp3 file]
Here's some fun, a mashup of three cadenzas of Grimaud, Abbado and Lubin for the 23rd Piano Concerto, first movement, listen to an mp3 created by John Clare here.
After all this, the 2nd movement is stunning and beautiful: