In favor of it being authentic: An iPad, such as a baseball or bat would be more difficult to sign than a paper such as a photo or contract.
Also, he is selling other Steve Jobs signed memorabilia. Those signatures look authentic.
What I'd like to see is the build date of the iPad. Perhaps the serial number would be an indication, but we don't have that information as the seller hasn't provided a shot of that screen (with the iPad turned on).
The engraving doesn't bother me as anyone giving instructions for the wording could have specified or the engraver himself could have made those slight modifications (capitalization).
Interesting item.
What would you think it would be worth if it could be proven to be genuine?
(I think his asking price is about right on the valuation and he isn't leaving any money on the table.)