Perpetual being cheaper after 10 or 15 years doesn't sound all that weird to me, I mean if you want a license with no expiration date, don't expect it to be cheap. And if they really want to do right, give a very serious discount on a perpetual license after you've been on subscription for more than 5, 10 and 15 years.
This will make much more people go towards desktop subscription I'm sure. Indeed not all but much much more will go that route, while keeping the perpetual for the rest available.