You can't have liked it that much for you to have not noticed it when looking at the car - before, during or after purchase for 2 1/2 months...?
Seriously though - it's a second hand 4/5 year old car - you can expect it to be perfect in every way, certainly when it comes to cosmetics. As already said the D/C finish albeit attractive is particularly weak and vulnerable. So even if they'd not been kerbed already they would need refurbishing due to corrosion by now.
If you bought it brand new you quite rightly should expect it to be original and as perfect as any other reasonable person would. That's why used cars are cheaper - they're not going to be 'perfect' unfortunately.
Of course I checked the wheels, but obviously I didnt do my research properly (slaps wrist) as I thought that the diamond cut finish is an optional extra not that all of them roll out of the factory with them as standard.
Once I slightly nipped the kerb, i realised that my wheels had been coated in paint and I could see the diamond cut finish beneath. So aa stated by a someone on a previous post as well as me, that the dealer instead of sending off the wheels at an expensive has done a quicker job to reduce costs and get them sprayed in-house.