I actually logged in to the forums to ask the same question.
I installed a Voom 500 Business line to my premises last week.
I had already a residential line cable with the Superhub2 so all the guy did was to unplug the cable from the SH, connect a splitter to the end of it, and from there two cables, one to the old SH and one to the 'Business' Hitron router.
This is DESPITE I had an unused cable hanging outside my wall ready to be used.
The technician (Virgin subcontractor company) reassured me that this the way they do it and there was no point drilling another hole to my (thick) wall.
I do have huge problems with speed on the Business line however this is due to the GRE tunnel and the static subnet I've been assigned. It's a known problem so I cannot blame the splitter practice... I do have an open ticket though...
If anyone else has solid argument that the splitting practice should NOT be happening please let us know.