On a slightly off-topic talk, I think the whole thing basically boils down to the crux. People aren't too bothered to change the looks of HN because it just works good as it is and that's most important. Now, ages from now Apple's design philosophy might look pretty old but may be people will be okay with that because it's a brand. I tend to think of HN like that.
Particularly its useful, if I have not used HN for some days, and come back to see 'what great items have I missed?'.
edit: minor rephrase