These applications try to be smart about where your cursor should be, but they aren’t perfect and often don’t account for every possibility. Or your banking/shopping website is coded by a moron and somehow you end up hitting delete and losing your transaction details when it jumps you between fields.
If you haven’t experienced this, you’re a more accurate typist than me, even more of a lurker, or using Chrome for linux (where it’s been fixed), but when I’m writing, backspace should mean backspace and should never delete ALL of what I’m working on.
Google has a number of open issues for this merged into: https://code.google.com/p/chromium/issues/detail?id=36533