If your adamant on a 4 stroke option, perhaps go for a Saito FG20 gasser. It may lack a little in power over the DLE, but you'd have the 4 stroke sound track that would more easily drag her around, and still have all the benefits that come from going with a gas power-train.
As for their motor choice in their promo video, I'm sure that with an vast supply of options for motors from Saito & Evolution, that they are going to install the one that best works for the given model. One where it is correctly powered, and not too heavy for that given plane.
I may be a little bias when it comes to gas, as even though I have two gas powered planes in the works (a H9 Blue Nose P51, and a 73" Sbach), I still have a nitro heli and a nitro powered Yak54 that have been my go to models for some time now ..... but I can say hand on heart that I'll never buy another nitro model, they will all be gas in the future as I cannot see any positive on going to nitro for anything I want to fly, gas always makes sense over nitro (to me at least).