I guess this depends on the initial type of the data which in the first position.
Not entirely true. (Try '130' + 1 + '120' => 251)
If you see the links I posted earlier, the key in this case is datatype precedence. It takes the operands and applies the precedence rules - in this case, the integer takes priority, regardless of whether it's first or second.
http://msdn.microsoft.com/en-us/library/ms190276 (operator precedence)
http://msdn.microsoft.com/en-us/library/ms190309 (data type precedence)