stty gets/sets IO characteristics of terminals, both physical and virtual. Because of this, it can set parameters that will have no actual effect, like the baud rate of a virtual terminal.
First you have to understand the types of terminal on Linux systems:
Most of the terminals you will see will be pseudo (virtual) terminals, and live in
/dev/pts. These are sometimes called ptys for short. Any sort of software terminal lives here, whether it be a remote login via SSH or a local terminal emulator.
A tty (
/dev/ttyX) is a local console emulated by the Linux kernel. This is the kind of terminal you use in Linux's virtual terminals.
getty is the program used to show a login prompt and start a shell on these terminals.
A serial or USB serial tty (
/dev/ttyUSBX) has a real baud rate setting, and corresponds to real hardware. This is the real reason
stty has a baud rate setting, and unlike virtual terminals, will be affected by changes you make to the baud rate.
sttycan just turn knobs that don't apply to virtual terminals.