Screen inches and real-estate have nothing to do with each other. Pixels. Only Apple links pixel count and screen size, and again, a 15" 1920x1200 display would offset the loss of the 17" to begin with.
That is pixel size but I find that on the smaller monitor the windows are made to be a little larger to make up for the smaller elements on the screen so they eat up more pixels.
Using USB power external monitors is not a solution I really care for.And you've been able to connect 2 external monitors to the MacBook since it shipped with the 9400m, back in 2008. Just need to be creative about how you do it.
Daisy chaining with thunderbolt isn't the only way.
Again, screen size and screen real-estate have nothing to do with each other. The 13" MBA is quite the proof of that, being able to have as much stuff on screen as the 15" MBP, albeit, without the fischer price look.
Again yes they do.
Just because you have the same number of pixels does not mean the stuff is going to be the same size. People tend to zoom in more on the smaller screens and as such eat up more space.