I think this is just speculation, a bit of conspiracy theory, and anti-MS to say they intentionally pushed out defective hardware. Over the last 25 years I have worked for several consumer electronics companies and they generally do not intentionally do this. Problems do come up, it takes time to fix and flush the manufacturing, distribution, and sales channels. MS and any other company know the real cost of problems like the ring of death and know that it cannot be just swept under the rug – if there is anything they can do to fix it they will.
I did personally have this happen to my 360. I called them and had a new one within 10 days. The support calls where the best I have ever experienced, no questions asked they sent me a box to pack it, picked it up, and sent me a new one. It was an inconvenience and I wish their quality control/testing caught the problem initially, but MS handled this better than any other consumer electronics company I have experienced. This just sometimes happens with complex consumer electronics – I just don’t think many of the people complaining about this to the point of lawsuit really understand this.