In the years since, I’ve only ever heard mention of older models, not newer ones which makes me wonder if this is a special case and situation where technology is frozen in time intentionally to foster learning.
Oh yes, they're frozen in time, but since the people who pay for them are not the same people who demand they must be used, they're not frozen in price. It's the most expensive kilobytes you'll ever buy.
At my high school we were allowed to have TI-83s but not TI-89s, because 89s had built in CAS (computer algebra system) and could do your algebra homework for you. When I went to college I already had an 83 so I didn't feel the need to upgrade.