Well, Annie, you got me researching online. Here's what I found. I think the fluff-factor in the commerical American mayo is due to the types of machines used to manufacter it at such high quantities:
"When you make mayonnaise at home, you whisk together egg yolks and seasonings (often lemon juice, salt, and mustard), then slowly whisk in oil until the mixture is emulsified. By contrast, the ingredients for commercial mayonnaise are premixed and then processed through a colloid mill, a machine that breaks the mixture down into tiny, uniform droplets and creates a stable emulsion with a light consistency. " -From: http://www.cooksillustrated.com/tast...gid=82&bdc=984
Homemade mayo will be far from buttery in taste, though, so I suggest you give it a whirl!
Personally, I'm a fan of a Japanese mayonnaise called Kewpie. I think Japan consumes more mayonnaise than any other country in the world. It's yellow and creamy and comes in these squeeze tubes. The taste is different from what you'll find on US grocery store shelves.