Let me address number 2 first.
2) Yes, it is possible. The champions of American football, the Greenbay Packers, are owned by the fans. There are some other teams I believe, but none come to mind. I prefer that system, and I am a fan of Tottenham Hotspur, who are also technically owned by the fans (though the owners control 88% of stocks or so). The reason baseball, though, has no teams owned by the fans is because of certain rules and practices. It's not technically illegal, but the Commissioner of baseball would probably never approve it. And yes, the Wilpons own the Mets and are dealing with being sued for about 1 billion dollars as well as losing money with the organization at the same time. The majority of Mets fans dislike the owners and would be much happier with them gone.
1) Yes, I believe it is a trend across baseball- I know it is certain for the Mets organization. The reason, though, I believe, is because baseball seems to have hit a certain ceiling. There are only a few teams who can spend more than has already been spent (Yankees, Red Sox, maybe Dodgers or Cubs?). Due to this, contracts have leveled out; on top of that leveling out, people are having more trouble buying tickets because of the ongoing recession, and teams are lowering prices (which they're able to do since contracts have leveled out and operation costs have remained the same), bringing more fans in for less individually but more collectively.