The original HP-42S calculator allowed the user to type a maximum of 12 digits, and displayed 12 digits, and so the 42s does the same. The TI you are using allows 14 digits.
The 42s is actually much more accurate then the TI because internally values are stored as 25 digit numbers and all operations are done in full 25 digits. However, your point is fair, especially given the internal accuracy is much greater. I'll look into it.