From my limited understanding, the difference is the government having a reasonable level of certainty that the device in question contains the evidence they're looking for.
The analogy I would use is a locked closet full of file boxes. If the government is certain that the files relating to a specific crime are in the closet, then you can be compelled to assist them in opening your closet or face an obstruction of justice charge. However if the police suspect you of a crime and suspect that you're the type of person who would keep the evidence in your locked closet that is not enough compel you to open the closet so the police can check up on their hunch.
In this case, I read it as the men are suspected of insider trading and the government believes that they would have used their cell phones to communicate about the deal and the phones contain evidence of such. There is no actual evidence that the phones were used and so they're not obstructing the police in obtaining evidence the police know is there, but rather preventing the police from poking around to see if the evidence exists at all.
I find it odd that they aren't just able to get the data from the carriers. The only reason it'd be on the device but not the carrier/Facebook/Twitter/etc servers is if they encrypted the messages, but they would probably mention this if it were the case.
The analogy I would use is a locked closet full of file boxes. If the government is certain that the files relating to a specific crime are in the closet, then you can be compelled to assist them in opening your closet or face an obstruction of justice charge. However if the police suspect you of a crime and suspect that you're the type of person who would keep the evidence in your locked closet that is not enough compel you to open the closet so the police can check up on their hunch.
In this case, I read it as the men are suspected of insider trading and the government believes that they would have used their cell phones to communicate about the deal and the phones contain evidence of such. There is no actual evidence that the phones were used and so they're not obstructing the police in obtaining evidence the police know is there, but rather preventing the police from poking around to see if the evidence exists at all.