You might read Consumer Reports - I think their most recent issue or the one before that had failure rates for LCD / Plasma displays. For most models I seem to remember numbers like 3-5% failure, so if you're on the high end of that and you have it 3 years, that's a 15% failure rate incident. Assuming the warranty costs $300, and an average repair is $300 and it breaks once if it breaks for someone, then for every $4500 they pay out, they take in $30,000. They're robbing people.
Buying an extended warranty, the vast, vast majority of the time, is a really bad idea. You're essentially betting against yourself when you do so - that something will fail. If you believe the equipment is that unreliable, don't buy it.
What you should do, though, is find a credit card that doubles your warranty for free. *That* is a smart idea - and you can't beat free.