I think this must be in expectation that the developer will type in some data which will then replace whatever is currently in the variable.
OK, that is good, but it would be even better if the 'default contents' (currently blank) would be the current value of the variable.
This way the developer can see what is in the variable. Right now, the blank box obscures the value.
To further illustrate the point, see the attached screencapture fragment.
The blank box obscures what is underneath.
The blank box even obscures the name of the variable..
I am using RubyMine 3.1 BETA