Amazon has credibly claimed that the Kindle Fire has 20% market share. The Nook also has some not insignificant share. Even adding up the also-rans will probably get 3-5 more percent.

This is important because there is an inflection point where you are not allowed to use your monopoly in other markets -- that might be at 95%, but probably not at 75%.

I am making no judgement on their practices -- just correcting market share and when they may or may not be within the law.