Is Japan any more prog-related than say The Cure?

It's probably because Sylvian worked with Fripp, and Barbieri joined PT 

They were included because of their music, not because their members were/are involved with prog bands. Actually, they were first added in Crossover, before I was pressured into moving them to PR. As to why they're here, I'd suggest listening to their music before dismissing them because of their association with New Wave (whatever that means). My personal opinion is that a lot of bands tagged as New Wave were way more interesting/progressive than a lot of the stuff included here, but I am also against flogging dead horses.

Let's turn this on it's head: had Japan been suggested for prog related today I'm fairly certain they would've been turned down. The only artists to get into PR these days are the ones who have made their mark on prog rock or similarly influenced it on a large scale.
PA was a very "lose" place back when bands like Japan, Mercury Rev and the likes were included, and we subsequently ended up with a lot of bands that shouldn't be here. Seeing as Max (the site owner) is the only one who can delete artists from the site, we are most likely going to see more of these threads 'Hey man! How come Mercury Rev and Metallica are here when Megadeath and The Tubes aren't?!?!???'
Best answer is: why start including bands because of mistakes that were made in the past?
The Cure were and are a wonderful and at times experimental post punk/new wave group, but including them because an act like Japan is here, makes no sense to me. I love both btw and could quite frankly live without Japan on PA (Iwould even prefer it - as it evidently sends the wrong message).

Mick Karn was a bass genius. I just need to think of him and bam his tone, sound and feel immediately emanates from back in my skull.

Well, my guess is that Japan were quite more progressive than the Cure, both by having more indicated prog influences (Rob Dean's Fripp-esque solos, some keyboard parts), and incorporating astonishing inventive playing techniques (Mick Karn's bass, and also Steve Jansen's drumming) that were quite progressive. Also, "Quiet Life" preceeded and actually most of the similarly fashioned new wave records, so they weren't really copying anyone at that point of their career, and IMHO they succeeded in escaping the new wave wagon sonically with "Tin Drum". Yes, their image and some lyrics (mostly on first two clumsy glam albums that also hid some interesting and imaginative moments) aren't really digestible for a casual prog rocker, and even some band members, but I'd say they were quite progressive for late 70s/early 80s Brittish band.