Just a little something I found. I have a cheap chinese PS3 gamepad (“SZMY-POWER CO.,LTD. GAMEPAD 3 TURBO”, not that it would say much though), which is properly recognized by the system, but not Steam. It turned out, the problem is with the device's permissions. For some unknown reason Steam and some games require joystick device to be world-writable. Pretty dumb, since there's only need to read what it does, not to tell it what to do.