Why would they do this? The Dolce geometry has changed.

[nuliajuk]

I read the difference as follows:
13mm (about 1/2") difference for 44cm size, (511mm - 498mm).
16mm (about 3/4") difference for 48cm size. (522-506)
15mm (about 5/8") difference for 51cm size. (530-515)
7mm (about 1/4") difference for 54cm size. (539-532)
10mm (about 3/8") difference for 57cm size. (566-556)
So, only the 48cm and possible the 51cm sizes would possibly require a stem more than 1cm shorter. The slightly shallower seat angle could be more comfortable on rougher roads, and since the saddle would need to be a little further forward to position the knee over the pedal spindle, it's likely that most people wouldn't even need a shorter stem.