My original plan was to use Eventbrite, but we decided to go with Kickstarter mainly because they transfer funds sooner - I wasn't looking forward to floating a catering bill on my credit card.
A Kickstarter also makes it easier for us to scale the event to match the funding. The more money that we get for this event, the more that we'll be able to do. That's something that people who are familiar with Kickstarter understand, but would take some explaining on Eventbrite.
Including sponsors would have also been more complicated with Eventbrite. People just aren't used to paying for a sponsorship with Eventbrite, but it totally fits in the Kickstarter model.
A more subtle benefit is the community aspect. Kickstarter gives me the tools to communicate with backers, give them updates and make them part of what is happening. It's easier to do things like ask people for their address (to mail out post cards) and ultimately, I think that people feel more invested in a project when they use Kickstarter. Which is important, since we want this event to be one where people can meet the original members of the Homebrew Computer Club and carry on their traditions and stories.