Actually, in this case I think your getting some pretty good advice from the dealer. He is doing you a favor.
Frequent oil changes is one of the best things you can do for your car.
Longer oil changes -- imho -- are primarily to superfically lower the cost of maintaining a new car to help soften the blow of higher car prices.
Since most people do not keep a car for very long, that may be ok -- but pity the poor soul who buys the car used. He pays for the reduced maintenance intervals....
That in the long run it can lead to higher maintenance costs -- to the point the owner might just opt for a new car (gee, who benefits from this?) -- it is hoped will go unnoticed.
I run Mobiel 1 Delvac 5w/40 in my '02 Golf TDI and change it at least every 5,000 miles (along with the oil filter). (And Mobil 1 15w/50 in my Prosche and change it every 5,000 miles too, rather than the 15,000 miles recommended by the owner's manual.)
While synthetic oils, compared to dino oils, are more resistent to break down and whatever other ills can befall oil they are not immune to these ills.
Synthetic oils get dirty, break down, get contaminated, gather in soot, water, unburned fuel -- with lots of sulphur! in the case of diesel engines -- lose the additives designed to help fight these things.
Unless the price of more frequent oil changes seriously impacts your standard of living, I'd recommend more frequent oil changes.
In my case, I buy a case (4 jugs) of Mobil 1 5w/40 from a local Mobil oil distributor (which is pretty affordable but I don't the cost handy to post) and take in a jug each oil change. (I do not bring in more than that because the tech insists on overfilling the crankcase. If necessary I top off the oil afterwards with some spare oil I keep 'hidden' in the car.)
Consequently, oil changes are very cheap. Also, I call ahead and make an appointment and at the appointed time show up with the car and wait so I don't even have to deal with getting a ride to/from the dealer to drop off and pick up my car.
For instance, I just called and made an appointment for this coming Friday AM (I'm off but apparently the dealer/service department is open) and will get my car's oil/filter changed around 5,600 miles since its last oil change.
Sincerely,
Rock Crusher (Oo.)