Whilst I agree with you to a point Chris, I think if you take Nairn's case as an example, someone who has just taken delivery of a £26k car after waiting 6 months for delivery, should at the very least expect that if the car develops a fault very soon after delivery meaning it has to stay with the dealer for some days, the owner should at least be able to get a car of similar size. Obviously if it's just for a few hours whilst your is repaired, then fine, an Up will normally suffice for a couple of hours.
Obviously no dealer would have a fleet of GTI's or GTD's at their disposal as courtesy cars, but if you need to have a courtesy car for a number of days, and have a Golf, then you should get a Golf / Jetta / Passat etc. i.e. something of at least comparable size to what you have, even if it's of a lower spec and engine size. People quite often choose a car because of the size they need for their daily life (i.e. carry kids or equipment around regularly, so (as the women say), sometimes size does matter

Who knows, perhaps if dealers were forced to keep more than a VW Up on their books, you might see some frenetic action in trying to get the issue sorted ASAP to get their own car back !