@ HP,
I agree that the marketeers could make things a lot clearer if they had a will to do so.
In the harsh commercial world the technical reasons are subservient to the business ones, unless you chose, and are able, to buy a Virgin Media Service with a coax broadband and a twisted pair phone line and kept your BT O line as well. You could then select whichever method you want, but at a significant cost penalty.
However I suspect that many busy non-geek people do not wish to know how their services are connected.
Sadly also they do not wish to measure the competancy of their chosen provider to supply the services they have paid for and, more importantly, how their provider reacts to both permanent and intermittent faults including the interaction with BT Openreach. The latter organisation has been forced into a code of practice which many find quite unacceptable, but are unable to influence the situation.
(BT O's practice of fixing or abandoning a fault in a 90 minute service period makes the eventual repair much more complicated especially when the returning engineers frequently do not know what has been done before. This approach does not encourage proper care of the network either. I believe engineers are chastised for "under performance" so there is little reason to expend energy on always following the best engineering practices.)
The marketeers play on the failings of human nature which is why they use weasel words selecting the criteria they wish to advertise such as cost and "up to" speeds etc. etc.
A recurring theme here are the difficulties some people find themselves in when their services have gone wrong.
In these circumstances the end users have to became involved sometimes just to get their ISPs and BT O to co-operate.
An alternative aproach by some ISPs when it is only a performance issue, is to make the end-users conversation process so diffcult that they just give up.
Kind regards,
Walter