is there any reason to believe taiwan made lenses are inferior to japan made lenses?
I remember reading about people complaining about made in china lenses (dont know about taiwan).
Canon farms out the lower cost mass produced lenses to Taiwan (18-55, 50mm f/1.8, ...). The lenses are designed for low cost manufacturing.
This does not mean that manufacturing quality is inferior, just that the lenses are not designed to be "L" grade construction.
Its likely that the high end lenses could be made in Taiwan, or most anywhere. Canon just wants to keep the high end stuff at home.
On the other hand, Nikon farms out assembly of their lenses to plants in Thailand. Some of the critical lens components are still made in Japan, and they cannot be easily outsourced on short notice, it takes years to tool, startup, and debug a lens plant.
Canon has been trying to get a lens production factory started up in Oita for two years now. Thats where the new supertelephoto lenses were to be made as I understand it. Its not fast or easy.