The problem is that "[i]f they've broken the law" is not such a clear-cut question. Sometimes it is (WorldCom), sometimes it isn't (Qwest): http://www.cbsnews.com/news/top-10-ceos-in-prison-whyd-they-.... This is especially true with white collar crime, where the difference between legal and illegal activity often revolves around intent. There is definitely the potential for the government to use white collar laws to keep meddlesome rich people in line.
Sure, but a jury trial is in itself a pretty disruptive thing. And it's very easy to bias juries against rich people, for obvious reasons. Even if the person is acquitted, it can be an effective way of keeping people in line.
Consider the investigation of Mark Cuban for insider trading, which didn't even result in an indictment or prosecution. I don't think it was politically motivated, but the mere possibility of that made a lot of people nervous.
A prosecutor isn't supposed to toss cases at a jury to "see what happens." The prosecution is supposed to believe 1) that the person actually did the crime, and 2) that a jury can be convinced of it. You can debate the specific thresholds of doubt for each of those prongs, but "I dunno, let the jury sort it out" is a very bad system.
