Re: Yes ..... But !!!!
Presumably, no, not all inside traders are caught. And we don't know how many investigations don't end in prosecution because enough evidence couldn't be found, and of those how many are actually guilty. We could find out how many prosecutions fail (if we want to do a lot of poking around in Lexis or WestLaw or something), but again we don't know how many are actually guilty. And we have no way of knowing how many escape investigation entirely.
That's easy to forget when reading stories about really stupid inside-trading schemes like this one — oh yes, telling your family is a great idea, no way anyone will notice that — or this.
An aspect of inside trading, as a crime, is that the barrier to entry is very low for those who are handed an opportunity. So plenty of fools will try it, and some of them will be caught. That skews the perception of how easy or difficult it is to get away with.
That's not to say it shouldn't be prosecuted; I'm in favor of that. But, yeah, the most probable world is the one where a large portion of inside trading, quite likely the majority of it, is successful and not prosecuted.