Forgot to mention in the earlier post - it appears the likely cause of this issue is something called "thermal expansion" - I'm not an engineer, so I can't explain that, but it seems logical since the outer glass is absolutely perfect - no nicks, scratches, etc.
I have a 43" Samsung plasma (model PN43D450), which has developed a spider-shaped cracked. It was not caused by physical damage, but was off warranty. The repair would have cost over $800 (on a $500 tv), so that was obviously not an option. While I had no particular expectation that Samsung would do much since it was off warranty, they asked me to send pictures, and the service rep insisted that if it was a defect they would try to do something for me since the TV was still relatively new (less than 2 years old).
Well, I had been reading online about similar service tickets, where they tell people to send pics to be reviewed by some "executive review board", and every time (even sometimes during the warranty period) Samsung has claimed (based on emailed photos) it was physical damage and did absolutely nothing for the consumer (they again offered to repair it for $800, though - and they were serious about that being a viable option). Are we to believe there is a conspiracy by hundreds (or thousands) of unrelated consumers claiming the EXACT SAME ISSUE? Doubtful, more likely Samsung prepping themselves for the inevitable class action suit that comes from companies making defective products and then not standing behind them.
I've lost faith as a consumer in Samsung, and have since bought a new TV (no more Samsung products for me nor do I have the time or energy to fight an uphill battle), but I think there is a bigger issue that they are trying to cover up on their plasma TVs built over the last few years. I've posted pics of my TV at crackedplasma.com (oh, I've put some of that time and energy into informing other consumers) - see for yourself or search "cracked samsung plasma" online and see how many complaints come up making similar claims.