The difference with TI's calculator was there was a social motivation/aspect to programming them. Everyone had them and it was very easy to get started.There are programming environments for the iPad but it is a lot harder to share programs as not everyone has one and even if they do they need another level of indirection to get the program. The calculator is also much more prevalent/easy to use in the classroom.

My first program was a quadratic equation solver that everyone at my school used. I remember a couple people tried to imitate and improve on my program but I crushed them with new features and a better interface. I don't think I could do that with the iPad.

The technology is also a lot more complex and daunting with the iPad. You have the paradox of choice in choosing how you want to program it. You can't easily share programs with others and TIBasic, just due to its simplicity and the lack of design knowledge and effort for the user interface is a lot easier for a kid to pick up and start using.

One thing that isn't mentioned in the article is that if you wanted direct control over the screen you had to program in assembly; I don't even think they had programming language support for it at the time. It made it a lot harder to use than the regular TiBasic.