"Well, it is about the idea. The idea is the seed. It is the kernel that is the start of something new."
There are lots of details in the execution, and semantically you can refer to those as "ideas," but that's not what people generally mean when they say "an idea doesn't matter."
The Newton had a custom mobile operating system in 1993 [1], by the way. The iPhone did all of those things in 2003, eight years ago.
So why did the iPad take so long? There's a lot of technology inside that took a long time to get right. No one brilliant idea can be pointed to that's the "seed" that made the iPad work. Instead it's hundreds of hours of design and testing and iteration -- i.e., the execution.
If anything, the Idea behind all Apple products is that style, presentation, and user experience matter. But even that idea is worthless without a good execution.
Of course, none of this decreases the importance of execution (see any of a handful of Android tablets for an example). But the market player that had these ideas first got a huge head start on executing them.