You've not factored in the cost saving of the Councillors equipment.
I work in a council in IT, Councillors get the following.
1. PC in their home
2. Multipurpose printer/copier/fax
3. Digital Camera???
4. Broadband connection
5. Routing equipment and associated security bumph to automatically encrypt and secure.
The cost of this and yearly upkeep is more expensive than a basic ipad with 3g.
On top of all the equipment they get in the home there is a support costs, where IT staff home visit to repair equipment, not ideal during working hours (seeing as most Councillors also have a day job, unless they are already techno confused pensioners).
So I can see how an easy to use ipad could be perfect! I have seen trials of blackberry's, not ideal when the average Councillors dexterity is about the same as your average 70 year old.