I read somewhere (maybe here) that the mesh is different and that it wouldn't give you the same user experience if you used old ones. Sound a bit weak and more of an excuse to sell more eartips.
So I thought it was BS too. I tried my APP 1 silicone tips on my APP 2 and it did make a difference. However, the comply tips on both gen 1 and 2 didnt make a difference too me.
I think its also based on the music you listen to. I listen to a lot of sub bass heavy music so when I heard vocals / highs, I could tell a difference between the tips but otherwise I couldnt really besides the APP2 having a lot better bass / mid response than the APP1's