First of all, calculators do not do mathematics, they do calculations. Calculators are designed to help you solve arithmetic problems in an efficient way.
So trying to argue about the percent symbol from a mathematical point of view as being a unit of measure, as in parts per hundred, is to miss the point entirely. It is accurate, but is it useful?
When doing practical calculations, % as an operator represents a ratio between two numbers. If I want to calculate 8.5% sales tax on goods priced at $45, I want so that sales tax = 8.5% of $45. And if I want the total price with tax added on, it is helpful to calculate $45 + 8.5% = $48.83, and do this efficiently with a minimum of keystrokes. This was accomplished readily by every calculator made since the 1980's.
How is one going to do the "add sales tax" calculation efficiently on a device like the above-mentioned TI Nspire? I know, you will do something like (1 + 8.5%) * 45. But what the heck? I'm not going to waste my time doing that. I will just do 1.085 * 45 and be done with it.
On the other hand, it doesn't matter much, because the Nspire is the wrong tool for the job. You are not going to carry an Nspire in your pocket to work out tax while shopping.