I honestly think the ones pushing for a 4 year change are just chancing their arm and doing a bit of scaremongering to boot. I haven't heard anything from my dealer and they are usually not shy at drumming up work.
I know for the mk4 1.8T the book said change at 120k miles, but INSPECT from 60k onwards. I think this changed for some of the later models to a shorter interval. TBH for my own peace of mind I wouldn't leave it later than 60k but I'm not convinced by this 4 year business, if I can be bothered I'll have a look in the book later - I suspect it will say something like inspect from 4 years onwards rather than you must replace at 4 years

Edit - Just gone out and got the book for an early 05 GTI AXX engine service book published 09.2004
@60k (then every 20k) engine cambelt is checked (petrol engines only)
@80k miles camshaft drive belt is replaced - 4cyl unit injector engines only
@120k miles camshaft drive belt is replaced (2.0L 110kW and 147 kW TFSI only)
@160 miles toothed belt tensioning roller is replaced

Every 2 Years
Brake fluid is changed
Dust and pollen insert is replaced (for vehicles driven less than 40k miles in 2 years)
Every 4 Years
The tyre filler bottle in the breakdown set is replaced if applicable
The sparkplugs are replaced for vehicles driven less than 40k miles in 4 years (not 147kW TFSI engine)
The sparplugs are replaced for vehicles driven less than 60k miles in 4 years (147kW TFSI engine only)
Every 6 Years
The air filter is changed for vehicles driving less than 60k miles in 6 years
The tyre pressure sensors (if fitted) are renewed

(thought the system on Golfs used the ABS sensors)
No mention of 4 years anywhere.