I'd suggest that its the Dealer trying to screw you over. Longlife oil is better for the Gti, yes it costs more, but then at least if its on Longlife to begin with the cost has gone to the Dealer and not to yourself. If YOU choose to swap at a later point to Time and Distance, YOU can make that choice at that time. To be honest a solution when it comes to servicing when it comes round would be for yourself to provide the oil (its usually much cheaper to buy it yourself, with a bit of careful sourcing).