I'm not sure what the problem is. When a form has the focus, backspace functions as normal.

They just borrowed from IE. It's been around so long as to be considered standard practice. I've lost a bit here and there when the focus was in the wrong place when the backspace was pressed. Sometimes I switch and do my typing in a text editor and then just paste into my browser when I'm done. This has the added benefit of providing an easy to use spell checker, oh, and being able to save and come back. Typing straight into text areas is for little stuff you won't mind retyping if the server fritzes and hangs just before you press the submit button.

/me pokes the Submit button on the comment form.

/me pokes the Submit button on the comment form again.

I don't think the backspace goes back when you're typing... If no form widgets are selected it goes back to Back though.

there is an extension called keyconfig which can override this.

Funny, I use the backspace key to go back all the time, but my girlfriend just lost a long email she was typing because the textbox lost focus and she hit the backspace key, she was so pissed and had no idea the backspace key even had this functionality.