This is a good example of the fact that all products live in an ecosytem, and the brilliance of TI was at least as much in marketing and sales as in technology. This is a great example of "stickiness" of a prouct and the retuns a company can acheive by getting products adopted as standards. These calculators are still a good fit, becuase they don't do too much. The challenge for everyone (TI included) is how to avoid being frozen here forever. TI has put out more powerful calculators, but the gatekeeps (teachers, standardized test administrators) have not accepted them (and from their points of view, for good reasons).

Upton Sinclair: "It is difficult to get a man to understand something, when his salary depends upon his not understanding it!"

I hope your software development lifecycle doesn't start with coding.