Does the same apply for Paris. Why go to France when you can go to Vegas? They too have a monorail
I've been to all 4 islands of Hawaii on multiple trips and I can say it's absolutely worth the trip. The natural beauty and incredible people make it a truly unique place. IMHO Oahu is a distant 4th out of the 4 major islands. Pearl Harbor is a pretty powerful experience and a must see. If I were giving out advice to someone visiting Hawaii I would say fly into Honululu and stay 2 or 3 nights just to hit Pearl Harbor and the north shore then pick another island or 2 to stay for a week to 10 days. Inter-island flights are relatively cheap and very quick so it makes visiting multiple islands easy.
I've never been to Aulani but it looks nice and is at least in a good part of Oahu mostly away from the congestion and traffic of the Waikiki area. As a DVC owner I would trade in there for a few nights to check it out, but it's gonna be quite some time before I'm willing to take my kids on that long of a flight. I would imagine it has been marketed heavily to Southern CA residents who are only about 4 hours away and the Japanese tourists who are a very big part of the tourist economy in HI. May have even been a test case for possible DVC expansion to Japan too. If sales to Japanese tourists in HI were huge they might have considered rolling out a DVC in Tokyo. Still might.
Hawaii is excessively expensive if you want to stay ocean front in a newer resort property. The Marriott next door is slightly cheaper depending on which room type, but it's in the ball park with Aulani. Actually, if you could rent DVC points for say $14 a point you could get a studio room at Aulani for as low as $250 a night which is actually pretty reasonable for a beachfront resort in HI. There are chain hotels in the Honolulu area where you can get a room for $100 a night, but they aren't real resorts. Just a room to sleep at night.