I don't see how Vodafone would have anything to do with it since it's not their job to develop software.
Sure they could pressure Samsung and what good would come out of it? None because Samsung doesn't give in to "peer-pressure"
Vodafone's prime directive is to provide services and make sure the devices they sell work with their network. The moment something happens, they report back to Samsung with the issue which proceeds to the actual fix.
Vodafone makes most of it's money with the services and not with the devices...that's Samsung's turf. Just a small percentage goes to Vodafone and not a very significant one.
From the economic point-of-view, Vodafone doesn't win anything with pressuring Samsung in launching ICS to the Galaxy Tab 7100. And Samsung is launching this update so that their contract of providing updates within 2 years is met. This update is basically a big "shut up" shout to Vodafone and their clients.
And they won't launch ICS to it because this device is not being sold anymore so there is no point (on an economic point of view) to launch ICS.
In conclusion: Vodafone can't do anything and Samsung doesn't give a rat's ass