You left out the DPI number for the 11" 1080p display.
Let me try:
Retina iPad: 264 PPI
13" Retina Macbook Pro: 227 PPI
10.6" Surface Pro: 208 PPI
11" Vaio Duo 11: 190 PPI
There is a difference but it is minor and I disagree with your statements you can't compare or that it doesn't even "get near". You'll be hitting the point of diminishing returns.
Let me try:
Retina iPad: 264 PPI
13" Retina Macbook Pro: 227 PPI
10.6" Surface Pro: 208 PPI
11" Vaio Duo 11: 190 PPI
There is a difference but it is minor and I disagree with your statements you can't compare or that it doesn't even "get near". You'll be hitting the point of diminishing returns.