wow, thats pretty interesting. Good info and theory.
I have a fair complexion and use sunscreen quite a bit. I have had great success with bullfrog spray-on no-rub sunscreen. It lasts all day, is sweat-proof & water-proof and doesn't require my hands to touch it at all.
I haven't noticed any correlation between the sunscreen and the decals, though there might be something to that. The decal on the seat tube was melting away simply because this is where my saris bones rack grips the bike and, over time, the jostling of the bike in the rack has worn away the edge. I pulled the trigger and took the whole decal off with acetone (craigs recommended remover) last Thurs night after looking at the bike and think about this discussion.