Ok, continues to be a lot of questions and concerns about transporting, tipping, laying flat, etc. So I thought I take a crack at it. I have experience in design/development and ship packaging (and resultant field issues), though NOT FOR TVs (but for other large electronics).
For RPTVs, there is no bowl of liquid or plate of marbles inside!
So yes you can tip or turn BUT.....
The issue is "shock and vibe" and how the product is designed to withstand it, and then in particular for movement (i.e. transporting) how the ship packaging is designed.
The TV is designed to sit on it's stand and support the weight that way. So you should not turn the TV upside down AND SIT IT DOWN. The structure of the TV is not designed to support it's weight that way. I assume that is obvious.
For transporting, again it is not what angle or side, IF you were transporting in a gravity free environment and could guarantee no shocks (i.e. nothing would hit it and it would not hit anything).
But since it is transported in a real world with gravity and with shocks and vibration, the ship packaging (i.e. the box, cardboard, styrofoam, etc.) is designed to work with the required ship orientation (for RPTV that is normal vertical) to dissapate and control shock and vibration transmission to the product.
There is a tradeoff between the actual product design and the ship packaging design. You could design the product like a tank, and then it would need very little ship packaging. However that raises your cost (and has other effects like the visual design of the product, eg. it's "looks").
For the RPTVs, open the box and look. Between the built in stand/foot and the styrofoam in the bottom, it is built to take shock and vibe from the bottom with the TV upright. It is NOT built to be transported on it's side (or upside down).
Anecdotes abound from people, who would swear you can strap it on a camel without the box and transport down a mountain side.
However you are just playing the odds.
I would NEVER transport an expensive (and "delicate") purchase without the packaging, and I would NEVER transport it NOT in the intended shipping orientation. By transport, I mean moving from one site to another site, not from one room to another.
So if you can't fit it upright in your car in the box, then you take the risk (and you might just be fine... but might not), if you want to lay it on it's side or take it out of the box. If I was a retailer, I would demonstrate the TV works in the store, and the tell the person who wanted to throw it in a car on it's back or w/o the packaging, that its your choice, but you forgo your 30 day no questions asked return policy.
If you are moving it up stairs and have to tilt it, NOT a problem, as long as you don't bump it into something.
Sorry for long disertation, hope it helps someone.