Without money, you can't afford the significant other that gives you essential economic support. Without money, you can't afford to eat well enough to satisfy your soul. Without money, you can't afford meaningful hobbies or sanity-giving activities.
Rich people ARE happy. If they don't think they're happy, it's because they haven't experienced any misery and don't know what unhappiness actually is. They need to wake the fuck up to what the less fortunate are going through. Only then can they realize how good they have it. I've met homeless people who are happy with the life they're living and well-off people who aren't. I respect the former way more than the latter.
So, in the end, happiness is a mental thing. Having just a little money, though, can make a difference in your mental state - if you can keep busy, you're not wallowing in pity. If you're rich and aren't happy with life, why not experience some adversity and live in the back of a van for a month or two to give yourself some perspective?
poor person alert ---
Boring and mundane signature informing you I'm on a Droid Now with more bold!Less italics due to bold.