That's why people are requesting is the site plan if they say they won't support it then the user should provide a sufficient time to withdraw their funds to get free bitcoin gold coins. If not then the site should provide an option to withdraw bitcoin gold coins later on. Still got time to withdraw funds to get free bitcoin gold if the site doesn't support this fork.
The Bitcoin Gold will never work. I've read on their thread that they are going to launch it with a premine.
They are claiming its required because they need to mine for a bit for the difficulty to stablise. But even if that was true, they could just burn the coins.
Regarding getting any airdrops/bitcoin forks, its usually as a bonus to the service. However normally if you buy something, after you buy it you aren't entitled to any dividends after the sale is made. Most likely nobody will get their bitcoin gold fork coins this way.