About the 'use' element

Hello everyone

It's the first time I post here and even if I'm working with the W3C
technologies for years now, I'm a true newbies about SVG. So my apology if
my question seems silly.

Recently, by working on a project that use inline SVG inside an HTML5
document, I have made a mistake when reading the SVG specification: I have
assumed that any valid child for the 'g' element could be a valid target for
the 'use' element which is a wrong assumption (see my bug report to Mozilla
: https://bugzilla.mozilla.org/show_bug.cgi?id=579550).

Beyond my own misunderstanding, I was wondering : If a 'g' element is a
valid target for a 'use' element, why any valid child for the 'g' element is
not a valid target for the 'use' element?

As a web designer I found this a bit puzzling to have to wrap an element
such as 'foreignObject' with a 'g' element to have the ability to reuse it
through a 'use' element.

Is there any technical, philosophical or historical reasons behind such a
limitation?

Best regards
Jérémie Patonnier
http://jeremie.patonnier.net