It also depends on whether Bell has the rights to air / carry a particular title via VOD with DD5.1 etc.
I had this problem with Cogeco also, but in my case not only no DD5.1 but many titles (this was a few years ago) were in mono. So, if the movie was in stereo, at least you could have used Dolby Pro Logic II for instance and got at least some kind of 5.1 audio... Not a great solution but better than mono....
I think you'll find that it's in the agreements and what type of copy actually gets sent to Bell that they can provide. If the box provides DD5.1, then it's generally not a technical issue.
When discussing the Cogeco issue with the CRTC, I was informed by the CRTC that audio was not in their scope of regulation. This may still be the case, as long as it's "understandable" seems what they're concerned with.
DAB listener 12/2003-11/2011 (DAB Off-Air since 11/2011)
HD radio Listener since 06/2010