Sorry to see HTC bow out but unless you are Apple or someone else trying to sell content then this is a difficult market I guess.
So my fag packet analysis of differentiating factors that might be necessary for Tablet success:
Google - Brand, Price,
Apple - Brand ++, Quality
Amazon - Brand, Content ++
Microsoft - Brand, Quality, Office, New Hardware++
Others - Price?
Ok, you grisly limey, what is a "fag packet analysis" and why does it make me clinch?