This is unfortunate, but....
Manufacturers as well as nearly every extended warranty program I've ever seen consider screen burn in an issue of ABUSE. Leaving a static image on screen (and yes, black bars count as a static image) is considered a form of abuse. What's just BS at this point is why manufacturers even put a 4x3 aspect mode in the set's software if they know that it could lead to "abuse". Aren't they tempting unknowing consumers?
Manuals for TV's (particularly CT rear projection) have stated this for years and years. Unfortunately, double E or not, you didn't read yours until it was too late. This isn't a case of the TV just failing and Samsung refusing to honor their warranty.
As far as the set costing $6000 goes, any more with consumer electronics you pay for performance and features, NOT durability. It's the same way with cars. I can buy a Porsche for $90K, but because it's $90K does that mean it will be more reliable than a $17K Honda? Not at all.
There are a lot of companies out there that will honor their products with really great warranties. Parasound gives 10 years. Several speaker manufacturers offer lifetime warranties. Best TV warranty I've ever seen is from Planar (they recently bought Runco & Vidikron), a really high end brand of LCD TV that I recently picked up. Their "Customer First" factory warranty is phenomenal: Two years, immediate full replacement. They send me, the dealer, a new TV and I put your bad one in and the delivery driver takes it away. That's it. A warranty like Planar's is unheard of in the video market because most sets are made by companies that are generally too big to care.
Personally, I would be really angry at the store you bought it from. It's awful if they didn't explain to the T what happens if you watch 4 x 3 on a plasma. I ASSURE you that they know what burn is in and how it occurs. It's ludacris for a store carrying a set such as that to not care enough about you as their client to educate you on your new TV!
I own a business, too (an A/V integration company), and, while I certainly would have made CERTAIN you knew what burn in was and how to avoid it, the absolute LEAST I would do with an accident like this is offer you a new one at my dealers cost. Actually, if it came down to it I would call my rep and beat him into getting me the replacement at a reduced rate, then I would calculate out the profit I made from your first purchase and then have you pay the difference. Sure, I would have made zero on your purchase, but that's only one deal out of the year. A solid business can live with breaking even once in a while and should want to see their clients taken care of. You might want to try to work out replacement options through where you purchased the set? See if they can work with you on a replacement. Where did you buy it from?
Lastly, while my remarks in this post may at times have seemed harsh or insensitive I assure you that I feel horribly bad for what you're going through. You invested in what you thought was going to be an exciting product for years to come, only to get 4 months and a big "Sorry". Please keep us posted as to what ultimately happens with your TV situation.
Best of luck.