As has been mentioned several times it is extremely unlikely that what any one person does will actually affect another
I don't believe that, nor do I think it justifies remaining silent. In a curved class, such as most 1L classes, it could very well mean the difference between a 3.7 and a 3.3 in a 4-credit course. Certainly, as the number of credits increases, it doesn't mean as much, but it's still something that they're getting unfairly and undeservedly at the expense of someone else.
I also don't agree with the whole "They'll get their comeuppance when they fail the bar or turd an assignment!" Neither of those are guaranteed to happen any moreso than the possibility of bumping someone down out of an interview or out of a scholarship range.
ETA: also, even in just OP's example, it wasn't one, but two people cheating. Even if one or two people won't make any substantial difference (which I still disagree with), that's assuming that it's only one or two people. If you saw everybody in your class cheating but you, would you report that?