The sprue is acceptable as long as it makes holds all the parts securely, essentially making them one (albiet complex part).
I recently asked Customer Service to check this model:
http://shpws.me/3qXa Their request with it was to make the original sprue a bit thicker, and to make sure that the wheel supports were thick enough to survive cleaning.
The other choice is to include all the parts in a (semi) solid bounding box. This model:
http://shpws.me/2FWG in the crate is much more acceptable to the production team than the two peices were as separate parts. (the main peice there is only a 1/4 inch cube)
The whole point here is that super small parts (of which I am a major offender) are extremely time consuming. Connecting units together with sprues collects them into larger peices that can be handled with much less work than the items themselves.
Now, one note: Before we get handed down hard rules.. please tell me "hey .. this model requires extra handling". I'll be happy to fix any of my models that are particularly troublesome. Simply put, we need more communication with/from the production team.