Watch a video of the iPad signs in action
Maybe this has already been said and this link posted--I haven't time to read all the posts here, however, the iPad signs make a whole lot of sense if you see them in action,
as in the video offered by this review.
Almost any product in the Apple store (iPods probably excepted) now requires that you decide on size, extras, and other things; this gets especially complicated with iPhone and iPads which also require the customer to decide on a phone company. How else can a person be told what they need to know about the coverage of the phone plan and the details of the different plans, or just what the cost of what they're buying will be depending on the options they pick? They could be informed of all this by an employee, but prices and options on different products change every two or three months and it'd be hard for employees to keep up. Also, such things are much clearer if they can be seen on a chart rather than explained verbally.
So, iPads to give customers any info they might need makes a whole lot of sense and is much more efficient, given the constant changes and upgrades, than constantly printing and changing out paper signs.
The little video linked above shows a customer touching on different options and the price of the item they're interested in changing each time, right there on the iPad to show the customer what getting this or that option would do to the price. A paper sign can't do that. Likewise, the iPhone "sign" allowed customers to check out phone plans and coverage and such, which people need to know--should know--before they can decide to buy or not, let alone what to buy.
I don't know if all these iPad signs are more or less "green," and I don't know how good/bad all the cables look as I haven't gone to a store to see for myself. But given how complicated things have gotten with iPads and iPhones and the phone company plans and computers with various choices of disk drive and RAM options, these interactive signs would seem to be not vanity or overkill, but a necessity.