Earlier quoted context omitted.
To be clear: This was always true (legally), and this decision doesn't change this. As long as it was not a custodial interrogation, and you had not been formally charged, your words could be used against you (ignoring other procedural evidence rules for a second) without Miranda or other warnings. The only thing his decision changes is a long-standing open issue of when silence can be offered as proof of guilt.
>> The things I don't say may be used against me >This was always true (emphasis mine) On the other hand, the fact that there was a SCOTUS case about it means that while it may always have been true, it wasn't clear to everyone that it was true.
The layman who hasn't had a brush with adversarial police investigation techniques and doesn't have an explanation for a (seemingly) factual assertion by the police may simply not know how to respond, knows he needs to tread carefully lest something get pinned on him, but is unaware that silence is not considered careful at this moment (since, if he remembers, he is talking to the police without being cautioned or under custody).