Looking at the underlying technology of C2 (HTML5 / Javascript), I notice that all variables are ultimately without a type in their definition: http://www.w3schools.com/js/js_datatypes.asp
In fact, at the bottom of that page it says:
"
Do Not Declare String, Number, and Boolean as Objects!
When a JavaScript variable is declared with the keyword "new", the variable is created as an object:
var x = new String(); // Declares x as a String object
var y = new Number(); // Declares y as a Number object
var z = new Boolean(); // Declares z as a Boolean object
Avoid String, Number, and Boolean objects. They complicate your code and slow down execution speed.
"
With that said, I guess the Construct 2 editor tries to at least provide some structure by allowing variables to be specifically set to number or text. It seems possible to add the "type" of Boolean, but they probably also decided it was unnecessary due to the ability of Javascript to perform Boolean checks for most data types ( http://www.w3schools.com/js/js_booleans.asp )
So, they probably figured it's easier to just invert a condition that checks "if X = 0" than to bother with all the extra code to support a fake type, that would lower performance during execution if it were enforced via variables declared as objects.