I seriously doubt the post title. Are you sure it's just not age?
The insides of a mouse are pretty generic.
Microsoft Wheel Mouse Optical
Show Image
(http://www.dansdata.com/images/moremouses/newexpguts440.jpg)
That's an Intellimouse Explorer 3.0
I blame DansData. (http://www.dansdata.com/moremouses.htm)
WHOAH - these things are oooooolllllllldddddddd......
Show Image
(http://www.dansdata.com/images/moremouses/mouseplague440.jpg)
Anyway, the switches are all 70g that I've ever found.
Are these PS/2?
Not sure about the logitech, but the Intellimouse 3.0, Intellimouse 2.0 (very rare), and WMO were all USB w/ PS/2 adapters.
(http://i1-gadgets.softpedia-static.com/images/newsrsz/How-to-Connect-an-USB-Keyboard-or-Mouse-to-a-PS-2-Interface-And-Viceversa-2.jpg)
First generation WMO's used an Agilent/Avago sensor, while later 2002-2003 models started using the STMicroelectronics OS MLT 04.