I don't think it's just that the performance case for middleware has become weak. It's also that traditionally you pay per connection some sort of license fee.

I don't think it's just that the performance case for middleware has become weak. It's also that traditionally you pay per connection some sort of license fee. So if you are running Oracle or SQL Server, and you want to add additional clients that, say, do additional process on notification, that means additional license fees. This isn't a problem on PostgreSQL. It means there are choices between the traditional ones of putting everything in the database or in the middleware.