eshell and tty numbers

This may seem obvious after reading more, but it surprised me a little that emacs eshell mode does not reserve a persistent tty number, and grabs one on the fly for any command run. If I have a terminal window open, using tty 0, and run the tty command in eshell, it may tell me tty 2, but after closing the terminal, running tty in eshell now gives tty 0. This is not the case with real shells, or even with the shell mode in emacs, where the shell has a persistent controlling terminal.