I think its Logitech realizing that with the mx518, they had a winner, as proven by the constant high demand and sales of the device.
I'm not saying this mouse is bad, it just lacks completely the innovations that Logitech has in its tray.
Good wireless, iperwheel, smartshift, sidewheel, 3 years battery life, optical buttons and so on.
It's a basic, good shaped mouse, nothing more that. And from this point of view is very overpriced.
Just compare it with an M705, great wireless, unifying receiver, 3 years battery life, a better (almost perfect) form factor, hyperwheel and so on and it sells for less than 40$...