[quote=@Shienvien]
<Snipped quote> Not on all systems... And we don't really have many multi-field forms here to begin with. 
[/quote]

But it's [i]expected[/i] behavior on a browser. Barely any browser-based form respects tab as an indent character. Accessibility for keyboard navigation, IMHO, is more important than a one-touch spacing key. If it's available via shift+tab or through manual whitespace, that should be an acceptable solution for a feature that is rarely used outside of document creation. 

EDIT: [@Mahz], do pasted tabs (from Word or otherwise) render properly? This may be another workaround.