Manufacturers definitely need to be held responsible for defects in their product. Again, I will use Toyota as an example. The frames Toyota used for the first generation Tundras were from Dana. When people started calling in complaining about their frames rusting out, Toyota didn't say, not our problem, call Dana. They took the trucks in and either bought them back or replaced the frame with a good one.
If this screen issue becomes a serious problem across multiple handsets (which I doubt it will), it's Motorola's fault for not thoroughly testing the display assemblies, even if Samsung manufactured them.
And I agree with essentially everything you've said. My point was, this display which was shown above was the FIRST incident I've seen reported, and quite a severe one at that. To use your example, if those Toyota owners were instead ONE Toyota owner, do you think Toyota would have replaced that one truck? I think not. It becomes an issue of things getting "too big to ignore", before action of that dramatic level takes place. I am sure that the first caller wasn't told "Frame rusting out, sure...bring the truck in and we'll replace it for free". I can imagine what that first call was like, and I can bet it wasn't pretty.
If there is a rash of problems, even if that rash is relatively small, it may still be enough to identify a "trend" in the problem and that will help to point to the cause, in your example's case the Dana frames. I would bet bottom dollar that Toyota didn't eat the entire cost of those replacements either. They most likely struck a deal with Dana to cover their respectively agreed upon portion of the costs to repair or replace.
Now, others have mentioned in this thread a "purple haze", so perhaps this IS a problem that will rise to the level which get's national attention. But as said before, and before this thread was started, I had not seen ONE complaint even remotely pointing to a "purple haze" issue. Granted, these are new phones, so they aren't nearly as prevalent yet as other phones, and perhaps the fact that this one phone surfaced this early is a harbinger of things to come. I do hope not, but if so, I am sure Motorola will address it once it becomes "too big to ignore". Until then, it's a standard warranty claim and like anything that is manufactured by imperfect humans, there will be a certain percentage that will fail right off the line due to imperfections.
Finally, the only true test of how a device will perform in the real world...is real world testing. Motorola almost assuredly did test those displays, as did Samsung, and I am willing to bet there is both a stated DOA failure rate, and a MTBF rate as well. If those two rates are within expected normal rates, then the manufacturer will approve the device and begin the manufacturing. There is no such thing as 100% perfect, and that is what recalls are all about.