i don't know, after a list of things he didn't do that he's thankful for, containing something he was responsible for in this way is a subtle nod to what he did create.
Its powerful because (a) he probably didn't explicitly add it, and (b) it references his impact on the world and (c) the iPad is obviously important but no where near as important as mathematics or medicine, and its not included on the list, just a helpful nod to its ability to help him reflect on this list.
The auto-marketing footer sullies the rest of his letter. The content recognizes all of the great achievements of human civilization and then at the end there is an advertisement. Which relies on it's continued inclusion in emails by stroking the human ego, so not very Buddhist, either.
Its powerful because (a) he probably didn't explicitly add it, and (b) it references his impact on the world and (c) the iPad is obviously important but no where near as important as mathematics or medicine, and its not included on the list, just a helpful nod to its ability to help him reflect on this list.