I'm sure the price of gold used to vary dependant on what tier you are on. You're right about android being cheaper than iOS. I wonder if it's cheaper in the US than over here in the cold, wet and frosty UK.
Here's what I see:
iOS level 100 - Vault of Gold £69.99 (approx $113.45 USD)
Droid level 12 - Vault of Gold £63.17 (approx $102.39 USD)
Im UK player and have an acct on each operating system and a vault on ios on sale is £55 droid £50 both with a few pence more, but £5 difference, can only assume apple make a bigger mark up, surprised at that? Lol
Its just the occasional unscheduled Gree discounted sale price guys on different platforms. Nothing else.