Most contemporary gameplay design is about complete control. Designers, level builders, and testers spend hundreds of hours making sure that their game plays exactly the way they intend. When players figure out something unintended it's usually a glitch or an exploit. Eve Online is great at giving players a lot more freedom than that, both on purpose and by accident. Buddy lists and instajumps are two kinds of accidents.
In Eve you're supposed to add your friends to your "buddy list" so you can chat to them more easily. But the buddy list turns out to be way more useful for tracking enemies, because the game helpfully tells you if your "buddies" are online. Did that pirate you're chasing log off? Add him to your buddy list and get an alert the moment he logs in again. Are you at war with Evil Mercenary Corp? Add all 100 of their members and watch for when they're offline and at their weakest. I'm confident when the Eve designers added buddy lists they didn't intend for them to be a surveillance tool against your enemies. But it is one, and so the game is a bit more complex.
InstaJumps are an unintended consequences of the design of the travel system. When you dock at a station or jump through a stargate you first warp there quickly, arriving 15km short of your goal. Then you fly slowly through those last 15km until you can dock or jump. You're invulnerable when warping, but in the 30-60 seconds you fly that last 15km you're very vulnerable to attack. However, Eve lets you warp to bookmarks in arbitrary points in space. So if you have a bookmark for a spot 15km past your destination then you can warp to that instead, landing 15km short of the bookmark or right on top of the goal. No more vulnerable slow flight.
Having good instas is an essential tactical preparation. They're a huge pain to make and maintain. People sell them for a lot of money on the open market and good corps spend a lot of time copying libraries of instas. It all feels like a horrible hack, but instas have become an essential part of the game because it simulates local knowledge of the terrain. Having a good BM set is like knowing the lay of the land. It gives you an upper hand over any unprepared marauding invader. It may have all been unintended, but the result makes the game more interesting and developers are on record as saying they're OK with the situation.
Designing a game requires defining all the laws of physics for a new universe. It's nearly impossible to get it right. Traditional game design tries to optimize by tightly constraining the rules and testing the hell out of it before release. The Eve developers took a different approach, building an open ended system with lots of possibilities and then refining it over time to optimize it. They're remarkably good at it and it makes for a remarkably complex game.