Yes, simply because publishers can do it. Doesn't have anything to do with used games. They have armies of bean-counters working to see how many nickels and dimes they can shake out of your piggy bank and still stay behind the legal line.

It would have made no difference.

Most people tend to ignore follow-up costs like season passes, DLCs and costs for online subscriptions when they are buying the "main game". The publishers are only catering that ignorance.

Gamestop is merely an organized, physical representation of the used game market. You've still got garage sales and flea markets where you can pick up used copies of video games. Let us not forget the online market as well. I think if you love the game, you will pay for the extra content unless it's very unrelated to how you play the game. Some publishers try to take advantage of the situation, which is business, but again, the value has to be there somehow.

Let's say used games didn't exist, we'd get cheaper games but I do not think DLC wouldn't exist, expansion packs have existed for years.

I really doubt we would get less DLC. Most gaming companies are greedy and would do it just to get even more money.

It wouldn't have made a difference for several reasons.

1. If GameStop didn't sell used games, then people would turn to online outlets such as eBay and Amazon or local mom and pop shops.

2. DLC was going to happen anyway because development budgets have gotten bigger with each passing generation while the user base for many franchises and genres have not. Something was going to have to give. Even with advanced technologies such as Unreal 4, you can't have a AAA game be bigger and better than before and still have it be out in 2-3 years without requiring some extra source of income.

No, it'd be inevitable, if Gamestop didn't do it someone else will. Or people would rely more on eBay.

DLC = expansion packs. It always existed

DLC would've happened. From a business perspective games need a way of double dipping.

With Movies you get the cinema sales, then later on the DVD/Blu Ray sales, then later on the network sales of broadcasting companies wanting to show the movie.

With Gaming you buy the game and that's it. DLC is just their way of getting a bit more out of their game, and even then they need to make more content to do so.