Button Property Values

The button property is suppose to returns zero for a left click,one for
the middle and two for the right.
Is'nt it a bit odd to have zero as a return value?

Microsoft has been using the button property in IE since version 4 with
different return values except for the right button which returns 2.
Would'nt it make more sense to either be compatible with IE or make a
completely different property for this?

-- Terry