Hi SpreedsheetCrusader
In your SUMPRODUCT formula, the multiplication of the two sub-expressions will yield numeric results, which SUMPRODUCT can interpret and add up. Both sub-expressions however yield logical results, so key here is the multiplication method you have used.
Sam's suggestion, by contrast, using two sumproduct arguments (essentially the x values and the y values). SUMPRODUCT, like many other functions such as SUM, COUNT, MAX, MIN etc, cannot compute the result using logical values. Numbers are interpreted as numbers. Errors are inherited. Everything else is ignored, so essentially without the double unary Sams formula would produce both x and y values as arrays of logical values, which SUMPRODUCT would ignore.
Hope this helps.