I completely agree with your assessment of the keyboard. I have not had any issues with it other than the keyboard. I have had the keyboard for a month and I treat the entire machine like a new born child and it has torn in the exact corner you describe. This is ridiculous for a 130$ piece of hardware. I found your post while looking for a way to repair it. I'm very frustrated with it. Clearly they have chosen an inferior piece of fabric. I have worked with composite materials for years and there are many choices they could have used that would have been bullet proof. It is either because of bad engineering or because of cost cutting that this is happening, and in either case I am left with a brand new keyboard that is torn.
I also see no mention of Microsoft being willing to replace it for free or repair it, and I know that you and I are far from the only two poeple who are having this issue. I hope they will own up to the problem and help us out. I am loyal to the brand and other than this problem, I can say with confidence that the SP3 is a complete pleasure to use, and I have had zero buyers remorse until today.