Well I think that is partially true. I tend to sand things on edge. And even with great dust collection when half the sander is off the object I do get dust falling into the crevice between the higher object where the sander overhangs. I usually just tap the sander trigger and use the sander itself to suck up the missed dust like a vacuum.
There are many other instances like when using the jigsaw. It is not that effective at dust collection and I could see where a table would help. I also have a little Pencil router that has no collection and for this the down draft table would be great. Also, the table may be for tools that are not or can not be connected to a CT or other collector, even hand sanding would be nice on a down draft table.