Technically they don't specify "synthetic".... it even says so on the stickers. It says the oil must expressly comply to 50X.XX, and that "most" are "synthetic", but I've never known any 502.00, 505.00, 505.01, 508.00, 509.00, etc. that wasn't labeled as synthetic but evidently there are some sold in Europe that are.
I think people hold too much stock in that word.... and the whole Mobil v. BP/Castrol deal some years back probably is why.
Now we deal with the same issue with essentially every other brand. When a Honda Accord requires the ILSAC spec xxx at 0W20, people will ask "is that synthetic?" and I've just about worn my eye muscles out rolling them.
In the USA, any oil that says:
ANY VAG spec
ANY MB spec
ANY BMW spec
ANY Dexos
ANY ChryCo MS126-33
Or is any of the following weights:
0w16
0w20
0w30
0w40
5w40
5w50
10w60
... will ALL have the word "synthetic" on the bottle.