I just updated to the latest beta of Chrome, and the backspace key stopped working as a keyboard shortcut for the Back button.
After a few times of stabbing the backspace key and not getting the result I wanted, I decided to go looking into what was going on here.
It looks like it all started with bug 30699, where someone didn't like the default behaviour. That led to bug 36533, when the people (like me) noticed the functionality they were relying on disappeared.
Now I fully understand that Backspace == Back is not the default behaviour of Firefox (on Linux), but it is a configurable option, and I'd had it enabled there for years. I think it all started with when I migrated from Windows to Linux. It's normal for Backspace == Back with IE and I think Firefox for Windows, and I've just developed the muscle memory for it, and I've never had a problem like what the submitter of bug 30699 was complaining about.
I look forward to it becoming a configurable option in Chrome.