Steemit could filter any and all of those services, including Busy, out so only what is posted on Steemit appears. However, I like that I can use the other services and have them aggregated on my Steemit blog.
A good future feature for Steemit might be to allow users to choose what, if any, of the other services appear on their Steemit blog. That would take a whole lot more mature design than is currently available.
I'd have to go double check, but I am not sure they can filter. I haven't looked closely at the record JSON for a post/comment submission to the block chain, but unless they expressly identify the source app, then no they can't tell where a post was made. They probably do, but it is VERY possible the records dont track this, since they pretty much all have to submit the same JSON to save a record. I could look, but i just woke up and cant be bothered right now :D