That might be the case for LifeHacker (don't know; don't use it). But the example in Tim Bray's post is Twitter, which definitely needs to load a lot less data than it's full interface markup on most navigations.

Lifehacker kind of looks nicer only loading reloading the story and not the whole page. I gives things an application feel rather than a collection of pages and saves a heap of extra processing, why run the code again to generate a header and footer and side bars constantly when the version the user is seeing is perfectly up to date.

The experience is slicker - if you run a search on lifeHacker, you can click through and browse the results without affecting the rest of the page (including the list of results). With traditional page refreshes this would not be possible.