I would say in general it is not common. BUT, to use one highly publicized recent case, Mark Zuckerberg, post-IPO will have a controlling share of the company (>50% voting shares). And consider that he is one guy, with >5000 employees, and investors that have put in several hundred million dollars compared to his $0. Sometimes you're just that good.
I will however note that an LLC is different than a C Corp. LLC's do not have shares of stock, their ownership is expressed in percentages or 'membership units'. Typically but not always, percentages are divided (especially early on) by the amount of capital committed to the company or the capital-equivalent of labor at prevailing wages. Additionally, whoever did the heavy lifting or was the mover and shaker in turning the idea into a company ppl consider themselves an employee of, often does take a bigger share (sometimes much bigger). Also, as noted by ktr above, if your CEO was there first, and everyone else is late to the party, well...
Bottom line, what is the likely exit strategy? If the company could blowup like FaceBook, you'll likely be happy with even 1% ownership. If the CEO is likely to sell out to the first $10M waved in his face, 1% would net you $100K. What would you consider a "win" in the end? Rather than talking directly to the CEO about ownership share, I'd be talking about his perceived exit strategy -- which stated or not, he's certainly considered. If he considers $10M, $20M, $50M whatever, a target or likely exit, what percentage of that would YOU be happy with -- regardless of his cut? If it takes 5 years to build a $50M company, would you want $500K, $5M, or something in between? The answer to that is the real answer to your question. Stop comparing who has what and focus on what YOUR exit is. If it's not good, try to hike it up, or bail. Life is short.