I hate to ever hear anyone say an occurence is normal. As soon as you become acceptive of something being a normal occurence, you move down a slipperly slope.
It's normal in the sense that it this is not an isolated event. Yes, it is obviously undersirable for the crew (needing to alter procedures) and airline (cost of replacement, aircraft down time, etc). I wouldn't necessarily say that safety was ever compromised.
With the FAA and Air Carrier certification, if something ever were to become a "normal" (to use your interpretation) occurance that would compromise safety, the FAA would issue an AD, possibly an emergency AD. There are checks and balances to the system to protect complacency.
On a side note, I just looked at our checklist for this occurance. It does not even state that the flight must be terminated, as many of the checklists do. It simply has the crew reduce differential pressure, and descend. Plus, depending on which pane of glass actually cracked, you might have to limit your speed. The decision to land would strictly be a crew/dispatcher/maintenance control decision
