Spot on, Bill. I've modified the original post with more accurate language.
Apart from optical quality, what do you see as reasons for L-series lenses? I can think of the following:
- Wider apertures requiring physically larger lenses.
- Higher build quality (metal cases, weather sealing, etc.).
- Constant-aperture zooms, again requiring larger cases than most users would prefer.
- Higher-quality glass for lower optical defects.
- Arrangements of elements/groups with improved optical performance, but greater physical size, than lower-end lenses at the same focal length.
Again, this is me pondering off the top of my head. Please correct me if I'm wrong.