Ridiculous.
If Lincoln had been born in Illinois (statehood 1818), he would not have been eligible to be President by that reasoning. He was born in Kentucky (statehood 1792), so then that made the difference?
Does it say in Article 2 Section 1 that American soil is the determining factor concerning "natural born" status?
Obama's daddy is/was a Kenyan citizen. That makes him ineligible to be POTUS.
Obama could have been born in Central Park on live TV and he would still be ineligible.
Yes, it would have.
Barry Goldwater's eligibility was called into question for this very reason, in 1964. He was born in Arizona, when Arizona was not yet a state.
A quick spin on your favorite search engine will bear this out.
Would that matter, Illinois was a territory of the United States since 1776