"...even side cockpit windows require a diversion from what I can tell. I believe the danger being that if cracked it no longer has the impact resistance (ice, birds, fan blades) required to warrant continued flight beyond the first, safe landing spot."
The way the story was written (for some reason the pictures didn't show up the first time I looked at it) they made it sound as if it was a minor crack in a window in the main cabin (the story mentions the captain coming out of the cockpit to look at it), which would seem to be less of safety hazard than making an unscheduled landing. For that situation, the diversion and landing would seem to be more to keep the passengers from freaking out. Now that I see the pictures, it looks much more serious, and I agree grounding the plane was likely warranted from a safety standpoint.