I don't think the essence of "playoff hockey" has to do anything with like, "oh the whistles are gonna go away!" or "its just tougher hockey!" Because evidently, you can't stop the Oilers PP and they are going to get PP chances (and they're a pretty tough and nasty team in their own right). I think the real thing that has sunk them in the past, and could sink them against a deep, defensively sound, very well coached team like Vegas, is that teams can really plan for them. There's a reason that when Edmonton gets knocked out, they run into a 4-0 wall.
In the regular season, its play one team one night, get on a plane, go play another team another night. You dont get that sort of strategic scouting or planning around specific players or schemes in the regular season. Just look at how goalies get figured out as series go on - Canucks only beat the Blues in the bubble because they had Binnington completely and thoroughly scouted.
Tonight, they just completely neutered Edmonton in the last 10 minutes. Edmonton had no organized, structured way to respond, and tried to force individual plays super hard which might work in the regular season when theres less matching up, but it will absolutely not work in the playoffs where the entire team has been watching your tape for a week straight.