That's quite interesting (and the replies).
I looked at this the other day and kinda agreed with Philly. But I've actually sat through it doing it's animation this lunch time, and it is VERY clear to me now.
Only one problem - my three 4-ways are wired so they go Bridge-Both(Parallel)-Neck-Both(Series)
That's how the Fender Baja arrives, and that's how I've done two more since (after much phaffing each time!!).
I really wouldn't want the series and parallel positions in the middle of the switch - I find it's much more useful having the more powerful series option on the end after the neck. It enables me to treat it like a standard three-way with an extra option past the neck :D
Oh yeah, JDC, parallel is the "standard" tele middle sound - there's nothing quite like it, you either love it or hate it. The series sounds much more like "add the bridge and neck together", it's fat and biting all at the same time - you can "hear" both pickups' contribution to the tone. I like having it there, but I don't use it a lot.