Another option for that wording "When ~ becomes blocked you may pay 2B and sacrifice ~, if you do destroy all creatures blocking it"

Actually it looks like we can just say "blocking it" even if it is dead before the ability resolves Abu Ja'far

Apart from minor interactions with first strike or triple blocking, when if this any different than deathtouch?

It allows it to interact with with "sacrifice matters" and only works while attacking.