In accordance to the manual, and manufacturing and strict shipping policies, the panel should never be tipped more than 15 degrees. That said, the reality is that sometimes they are.
The panel was never designed to hold the weight of the electronics, and vica verca. At no time - technically, and to directly answer your question - should the panel be on its side. If it is, does that mean it's "automatically broken"? No, it doesn't. But it can significantly increase the risk of breaking in that position.
To answer the other question about manufacturing, the panels are kept upright from the plant, straight into boxes, and loaded on pallats upright. Shipping and distribution are aware that plasmas should always be upright, and outside of the rare careless warehouse person that might lay one down, I would be content in saying that they do remain upright as intended.
That said, people do it, and in most cases based on reports I've seen in the forum, it turns out okay, and in some cases, the unit is damaged. I did a quick Google search also, and was shocked that I found a salesperson actually suggesting that "it doesn't matter". I don't expect the average consumer to know this, but I do expect salespeople to know that it does matter.
The salesperson's pitch about standing it upright for 24 hours doesn't make sense. That's like shaking a lightbulb so hard that the filament breaks, and then saying that laying it a certain way will make it all better. I'm curious to what logic led that salesperson to draw that conclusion, but it's unfounded.
I both marvel and cringe when I see people load plasma panels in trunks. In those cases, not only is the panel on its side, but the plasma panel has additional pressure on one part of the glass where it sticks out against the top of the car's bumper. Whenever I see that, the only thing I can think of is, "If that driver hits a bump, that's a return. And if it's a Samsung, I hope they don't blame our manufacturing". The reality is probable that they arrive home okay and work fine. But I can't help it - based on the manual's recommendations, the box's "This Side Up" label, and what I know about plasmas, it's a risk.
If you get it mounted on the stand, or on the wall and it works, you're probably okay, and Samsung will cover it for a year (An additional 3 months if you register online). But if you have concerns, they are valid and I would recommend addressing those with the store management. Think ahead of time what would make you happiest - an exchange, an extended return policy, or even a discounted protection plan and discuss it to resolution.
Does that help?
Keep me posted!