Provide drop-down list of businesses in block query

If I do a search on classifieds in the asset manager, I get a drop-down list of business names. I can narrow the list by typing the first few letters of the name. However, if I'm setting up a query for a block, business is just "equal to" a blank line. Apparently undocumented is that you can put the business ID in there, but it's not obvious how to find the ID. Why not provide the same behavior as in the asset manager?