SMS just works. (except when it doesn't)
SMS just works. (except when it doesn't)
Steam is SMS, and I heard they now have a shitty custom 2fa but what you're describing is services that don't use an established standard, which is compatible with hundreds of established clients. SMS isn't merely nonstandard (and now deprecated), it's more expensive for both the user (requires an active sim card) and the server (requires sending SMS to numbers all over the world).
The custom component makes sure that marketplace activity is valid (somewhat like the custom banking dongles you get that require both your pin and some transaction identifier).
They'd be better off allowing the option of standard TOTP auth for login, so users can use a standard authenticator app, and then layer on a custom app for trading if needed.
1: http://steamcommunity.com/discussions/forum/0/49463187366895...