Having tremendous success with their first Kickstarter likely helped them get favorable terms when they raised their series A, but that applies to any company, not just Pebble.
I don't know what the terms their Angel investors got before the Kickstarter, and I'm not familiar with what is 'normal' for SV angels to get. I do know that YC startups fork over ~10% of their company for a few hundred grand in cash, but YC brings a wide network of connections and social signaling for future capital raises to the table.
Even it was just cash and no YC connections, if I were thinking about starting a young hardware startup, (if it were offered), I'd still probably trade whatever % of my early stage startup for the few hundred grand necessary to be able to hire the handful of right people and get to the point where I had a 'good enough' prototype + software to take to Kickstarter and (hopefully) get enough cash pledged to manufacture and ship a v1 product.
Of course, you could work a day job and save back that necessary cash and then fund the startup yourself and keep 100% of the company. Or be already independently wealthy. Or be a savant and do all the work yourself. Or get a traditional bank loan. Or some combination of the above.
But the SV way of trading a relatively small percentage of your company for an initial cash infusion of a few hundred thousand dollars is a valid option that many people would love to have.