I think the 'pow' field refers to 'proof of work' and thus is a mining related parameter (mining no longer occurs as far as I know). The account_creation_fee and other parameters there are the same as are currently set by witnesses, so I presume they are a record of the value at that time.

AFAIK the blocktrades team were involved with Bitshares before Steem existed, so it makes sense they would be earlier recipients of the Steem tokens.

I'm not sure what the empty named accounts is about - it's an odd one!