Notice that in most of the rest of the cases we will read in this unit, the government is arguing that whatever it has done does not constitute a "Taking" and the property owner is arguing that it does indeed amount to a "Taking."
Causby--partial trespasses through lower airspace are (or are not) takings
Loretto--small physical takings are (or are not) takings.
Penn Coal and the rest of the "regulatory takings" cases--regulations that reduce the value of private property are (or are not) takings.
The reason for this being the fighting issue between the government and the property owner is obvious. No?
If the government "takes" private property it must pay just compensation under the Takings Clause. If the government's action does not amount to a "Taking," then the Takings Clause and the requirement of just compensation does not apply (and the entire cost of the "non-taking" will be born by the poor property owner).
Josh ("it's a Taking") Duncan and Becca ("it's not a Taking") Duncan in jolly old London (photography by yours truly)