Also Titanium is naturally non-stick, so easy to clean in the field with no coating to wear off. And the lower conductivity means that you don't burn your lips on a mug like with aluminium or, to a lesser extent, stainless. And it doesn't effect the taste of water.
I have a titanium mug and it's a revelation! Go and pick up something in a camping shop and see how freakily light it is. Then consider the other benefits, and you should see what the fuss is about.
Kelly Kettles are not something I would backpack with, though, too bulky. In a car or canoe-based trip the weight would not be an issue, so the very high cost of a titanium kelly kettle would probably not make sense.