>Is there a reason for this limitation.

My Dad asked me this just other day. I figure its the OO side and the non-OO side of Fox colliding. I don't know how other languages deal with it.

>Why the distinction between allowing the object itself to be passed by reference, but not an object property?

The difference is between variables and properties, not so much objects and properties. Variables can be passed by reference or value whether they are a simple type like a string or an object. Properties can't.

To pass your property by reference, store it in a variable, pass the variable, and set it back.