This is technically true, but I've had the Starwood Personal card 4 times and the Business card 3 times and every time I got the 10k bonus. I just got the personal card bonus again last month. The secret is not giving Amex you SPG #. If they have to create a new SPG account for you, they must assume you haven't had the bonus before.

I had the same success with the old Platinum Hilton card using the same technique. I was also able to get the bonus the first time I applied for the new version, but I haven't tried to get that one again.