Can't see it myself, main dealers stock various different spec oils for different engines anyway and given 502.00 is also cheaper to buy in bulk, I very much doubt they'll use something that was over-spec for a fixed service if there's money to be saved, even if it did save them a tiny bit of space.
Not sure about SEAT fixed/variable pricing yet but a couple of months back I had to service my S4, and as it was the first service I'd had done since buying I wasn't sure if it was on fixed or variable so got prices for both from the Audi dealer with a breakdown of the oil cost as I usually supply my own. The dealer quoted two significantly different prices for the variable long life oil and the oil they'd supply with the fixed price service (about £50 difference for ~7L), so either they do actually provide the right spec oil for the relevant service or they're blatantly conning people which I find hard to believe.