As a new user to steemit myself, I was also initially confused by the steemit system particularly in relation to voting. My understanding is that people who have more steem power (and in general reputation) have been on the platform for longer periods of time and have actively contributed to community. As a result, they have more intricate knowledge of niches within the ecosystem which is steemit, and hence can help curate the best posts to get the most attention without an agenda other than seeing the community grow. If everyone had the same voting power, I feel as if the altruism and genuine interest users show in the community would be partially lost to money-hungry individuals, which is detrimental to platform itself.