Voda could lock Symbian-based devices if they wanted
"That should leave Vodafone knocking on Symbian's door - the operator has already developed a Symbian client for its '360 service, so surely it would make sense to use the newly-open Symbian for handsets locked into the Vodafone 360 service?
Except that such handsets wouldn't be locked in at all"
There's no reason why Voda couldn't create locked down Symbian devices. NTT DOCOMO have been doing it for years. The Symbian Foundation license doesn't restrict any use of the code. It does restrict use of the logo/brand if the device doesn't meet certain criteria, but:
(A) I think you could lock the device to other webservices and have a good claim to have met the criteria.
(B) I doubt Vodafone would care if they couldn't use the logo. It's not as though LiMo provides any brand goodness; so clearly that didn't come into the equation.
So the decision to go with LiMo over Symbian (which is very interesting) has something else behind it.