In most role-playing games the trope of classes is warrior/rogue/mage. In Shadowrun, it's samurai/decker/mage. Why replace thieves with hackers? Because not only are deckers doing the stealing, but everyone on the team is expected to have physical stealth skills, while only deckers have the expertise and tools for consistently (though not always) getting past your average megacorp's state-of-the-art security systems to shut down surveillance cameras and wipe away the group's digital trail, which serves as a decker's own unique brand of stealth.
Fridge / Shadowrun