Dallas has an exceptional mix of older guys, (Pavelski, Seguin, Benn) current guys (Robertson, Hintz, Heiskanen) and future guys (Harley, Stankoven, Johnston). They have a solid pipeline (Bourque, Kryou), have all their 1sts, and have an incredible track record of drafting and developing even if they are not high round picks. Also, they are one of the teams, like the Coyotes, who have never received a 1OA, or 2OA so no free gifts like the Pens were showered with.
Vegas is just a pure butt kicker and manage assets better than any team in the league. They are not emotionally driven like the Pens, Sharks, & Capitals have been and will not hang on to players longer than they should.
Both are examples of elite organizations and are managing their teams in a way that makes them competitive now and in the future and thus, no cause to believe they will have to tear down and start all over in the future.