I've worked in startups my entire adult life and, please take my word for this, there is nothing magical about startup bosses that change the dynamic between employer and employee, and there are no special obligations startup employees shoulder.
If you give 12 months notice, you should prepare to be marginalized in your last year at the company. If you give 2 weeks notice, you should not expect to be blackballed in the industry. If someone gives you a bad reference for giving "only" 2 weeks notice, you should urge your friends never to work for that person again; if a prospective employer makes a stink about that kind of reference, you should avoid working for that employer.
Tech startup employers are fond of a "third-prize-is-you're-fired", "reward for just OK is a severance package" mentality. They don't feel like they owe you a year's advance notice about their plans. Stay professional, but don't bend over backwards for an employer unless you have a specific, personal reason for doing so. "That's how it works in startups" is not a valid reason.
And please, please remember: it is a seller's market for talent.