A market maker is basically someone who provides liquidity on both sides of a price point, so users who want to buy/sell tokens will have someone to sell/buy to/from.
An automated market maker basically provides a way for the SMT creator to pre-load liquidity in the market, so there are tokens available to buy/sell around a price point.
It is different enough from STEEM/SBD that I wouldn't recommend comparing them.
Technically a STEEM whale could become a whale in any SMT by buying up a lot of the SMT, but that would give the SMT a lot of value (because of high demand) so in most cases that would probably be a good thing. I think SMT communities will be hoping that whales take an interest in buying their tokens, to make the value of their SMT go up.