How bizarre.
I've never seen cornstarch in a BFCC recipe before. I also checked with a friend who makes them and thinks it is a weird as I do. All of my German language cookbooks use a gelatine-stabilized whipped cream (they use leaf gelatin, not the powder stuff used in the US).
Sounds like they're substituting a very durable whipped cream shell for the delicate traditional frosting. It would certainly work, but the texture and taste is not going to be authentic. I guess that's the tradeoff they're making to make it more durable and longer lasting.
If you're worried about stability sitting out, there is Dr. Oetker's Whipped Cream Stabilizer than you can add to the whipped cream to make it hold up better sitting out on the buffet. I see it in specialty stores locally.