I have no particular details about this incident but I can comment on the abnormality itself, the cracked windshield.
I don't think that's a very "common" event statistically speaking but I guess the word "common" was used by easyJet corporate communication just to take the drama out of it.
Usually cracked windshields/windows are in the newspapers so just google it and count
A cracked windshield is not an urgency, not even one of our "LAND ASAP" abnormal procedures.
Very briefly, A windshield is made of a number of layers of toughened glass + others (polyurethane, PVB, heating film...).
When a crack occurs, a pilot is unable to determine which layer(s) has been affected, thus the seriousness of the situation.
Procedure in that case (A320,A330) is to make a precautionary descent to FL230 and to maintain a delta P of 5 PSI.
Depending on your route, a descent to FL230 can considerably reduce your options (fuel, obstacles...) and will affect your decision making.
Immediate landing is not necessarily required for a cracked windshield.
I won't be able to tell you why the crew elected to divert to ZRH, I am missing too many parameters for that.
You would be surprised that an A320 aircraft is actually dispatchable for ten flights with one of its external windshield ply cracked...
Hope it helped a bit.