There happens to be stock left, but you're overlooking something: what if there wasn't stock left?
Nine iPads isn't a huge number, which may make it difficult for you to see what the issue is. Let's say that you and 3,000 other people had the idea to try and make money off of resale of iPad minis, and everyone bought nine iPads. Now there are 27,000 iPads that are removed from the supply, and that are being sold at a higher price than Apple lists them for. If Apple produces enough iPads to satisfy demand and overcome the temporary loss of those 27,000 iPads then this isn't a particularly big deal.
But for the sake of example, let's say that supplies are so constrained that the purchase of those 27,000 iPads wipes out the supply in many areas. If someone wants an iPad, they'd have to buy from you or another scalper. At this point, they have two choices: pay you some extra money to get that iPad now, or wait until Apple produces more. In both cases they are being forced to spend something (money and/or time), and this is an expenditure that would not be necessary if the scalpers had not bought up iPads.
There's a slight difference here, though. Tickets are an absolutely fixed quantity, since seats in a stadium can't be manufactured. If they're sold out to people who legitimately want to go to that concert, then it's tough luck for anyone without a ticket. However, what if a large number of tickets were bought up by someone who didn't intend to go to the concert, but who simply wanted to make money off of those who did? I hope you recognize that such an individual is not enabling you to go to the concert by offering those tickets for sale; rather, if that individual had not bought up those tickets, there's a chance that you would have been able to purchase a ticket without having to pay a marked-up price. These types of people (scalpers) are widely recognized as being nuisances, which is why many countries and states within the USA have made the practice illegal when it comes to tickets.
As for the comparison between Craigslist and eBay, I've done quite a bit of selling and shopping on both. While scalpers may use them as selling venues, the vast majority of listings fall into one of two categories: cheap crap (sometimes knockoffs) manufactured in China; and used items. The former tend to dominate eBay, while the latter are on Craigslist and come either from people who are moving or who want a bit more money and are selling things that they don't use anymore.