LWN's primary audience is also people who communicate professionally via mailing lists. They just don't go for flashy sites, and prefer stability and consistency to whizz-bang prettiness - which is why there's an article warning folks to expect some changes and describing the reason why.
But the kicker is, whether or not someone thinks the site looks professional, it's a subscriber-based service that's been running for nearly two decades, that has hardcore professionals subscribing to it. It's not FOTM.
I wouldn't say that it comes across as unprofessional, though — rather the opposite. To me, LWN appears to be professional: no-frills, focused on substance over form.