The two possible reasons for Vodafone not handing out details were quite simple:
1. They wanted an easy life. Every single user has the same equipment at the end of the connection. This makes technical support 100x easier as you are dealing with known kit on each occasion. Threatening "no support if you're not using our equipment" is just that, a threat.
2. Vodafone's ADSL offering is in fact tiered fibre. So pay for ADSL, use your own equipment at get a 40/10 fibre connection instead.
I did read through the Vodafone forums, not sure of the "tin foil level" theories behind the reason - I couldn't spot any.
The former is accurate, the latter is tin foil territory. Fibre availability is lower and wholesale cost higher, have a look at BTO's wholesale pricing and then explain to me why a reseller pitching at the low end of profitability would shoot itself in the foot by artificially reducing its availability and increasing its costs?