Thanks all. Don’t get too hung up on those two particular examples, the trending for price is something I’ve seen across a lot of cars, not just those two. I reckon the correct answer is as above, more people want an A4.
I’m quite happy with a diesel, after ten years of owning two diesels (one of them an Audi), I’d never go back to petrol.
I have looked at BMW’s, comparitively poor spec in the 3 series, nicer in the 5 series but they hold their price well.
And as always for me, whatever car I get will only really get used for long trips. I cycle to work for the most part and do most of my shopping and short trips by bike.