[jonnathanson]

It's certainly not necessary, but my guess is that it follows from the "Don't Make Me Think" school of UX design. If a majority of consumers have been conditioned to expect a credit-card-selection menu (or series of clickable icons), then the absence of such might confuse them and cause measurable drop-offs in the purchase completion funnel. It seems a little farfetched, but I'm sure at least someone has done the tests and proven this to be the case. (And if not, then there is truly no reason for the continued presence of these menus.)

Anecdotally, I've noticed that more and more sites are using autodetect features based on the first 4 digits entered. It certainly didn't put me off as a shopper; in fact, I found it a lot more elegant. But I'm an unusual guy, as are most people who work in tech. We can't assume that what's appealing or efficient to us is necessarily the same for the broader masses.

[danudey]

I worked for a company which sold goods online and ran their own shopping cart. We took out the 'card type' drop down and just auto detected it. We had a bunch of greyed-out logos and once you entered a valid credit card number it would light up whichever card type it was (Visa, Mastercard, Discover, Amex).

What we found was a huge increase in people typing 'Visa' or 'Mastercard' into the 'Name on the card' field (whatever the field was called, I don't remember). People were so used to having to provide that information that they began to provide it in lieu of providing the cardholder name at all.

Think about that for a second; they stopped putting their own name anywhere on the credit card form, and instead started putting the card type in that field. Conversion went down, customer service issues went up.

We added the field back to the form, even though it was never checked and did nothing, and it resolved the issue.

[danieltillett]

We do a similar thing here in Australia with states and postcodes. Except for a couple of unusual postcodes the state can be predicted with a 100% accuracy from the postcode. We found that if we didn't include the ability for the customer to select a state then they would do silly things like put the state in the street address or even their own names. We added a functionless state dropdown and these errors stopped.

[jonnathanson]

Fascinating. And it makes sense. Sometimes long-time purchasing habits are hard to break, and forcing a change hurts results.