To me it fits in and makes perfect sense that wealthy and successful business people support the Democrats. I don't think the Democratic party could exist without that, so it doesn't make sense to me to wonder why they do.
It seems to me that the Democratic party, its candidates, and members are into saying one thing, but often meaning something different & typically contrary to what they say, from how one would interpret it. They seem to act like a game of semantics, denial, and cognitive dissonance, is logic and reality (I wonder if there's a way to find out what's really going on in their heads).
It's beneficial and advantageous to wealthy and successful business people, because it's consistent with their agenda to keep them wealthy and powerful, while at the same time making many voters believe that they're their friend. This is what salespeople do, especially the ones you can find at your local corner car dealer do, in order to try to get you to buy a car from them. By smiling at you and acting like they only care about you, the average Joe voter, politicians are trying to gain everyone's trust.
They do this to keep their loyalty and get them to look the other way so they can get away with all the crap that they get away with. This, along with the help of the media which is owned by these wealthy and successfull business people, is why when whistleblowers expose their corruption, or people call them out on their hypocrisy or broken promises, it seems like no one cares. In fact those who call them out on their hypocrisy are subjected to things like either being ridiculed, being labeled as insensitive to caring, or ad hom attacks (e.g., if you criticize Obama for something he does, it must be because you're a racist).
The wealthy and successful business people benefit because these politicians pass laws and run the government in such a way that's advantageous to the wealthy and successful business people. It's difficult to elaborate on this, because there are many incidences and a lot are relatively subtle. It's one of those things that's best done by observing what politicians promise and compare it to what they actually end up getting accomplished. Basically, whatever the politicians do, the wealthy seem to somehow manage to slip out of whatever clutches one might perceive being placed around their necks by the government. They have to play by their own rules, though; and you might notice that one also has to be a member of the club, otherwise they'll get "shunned" (e.g., Madoff).
This doesn't necessarily apply only to Democrat politicians, and there are even some decent Democrats out there that I highly respect (even though I might not agree with some of their political principles), such as Dennis Kucinich, Cynthia McKinney, and James Traficant. It does apply to Repubicans, in a similar way; in fact it probably applies to most Republicans (primarily the so-called "neocon" and "rino" variety). I don't really know which is worse, the typical Democrats or the neocon/rino Republicans, but I do think they're both bad.
