There might be some rationale behind the survival of this practice. You see, the user likes to be sure: when the site works the way (s)he expacts, the user is

There might be some rationale behind the survival of this practice. You see, the user likes to be sure: when the site works the way (s)he expacts, the user is happy. When it doesn't, the user gets frustrated. When the program gives the user text field of arbitrary length without giving explicit instructions how to fill it (i.e. "no dashes or spaces") the user might be just a bit afraid if the computer will parse the number correctly. Credit card number is sensitive financial information, and people are not likely to be comfortable with making second guesses about entering it. Probably the freedom of entering the 16 digits the way user wants just doesn't outweigh the benefit of knowing that the site will behave the expected way by any significant margin? Or those programmers (designers?) might just be incompetent. P.S The "4 text boxes" solution (with or without auto jumping to the next field) might survive because of the same reason too: It elegantly reminds you about the format of data you are allowed to enter, so you can be sure that your input is parsed all right.