True, and the fact BT operates as a group of companies is primarily to ensure it can demonstrate compliance with the regulatory requirements to provide equal access to wholesale customers.
My experience is that small ISPs are much better at getting information from BT Openreach and BT Wholesale: you can talk directly to someone who has direct access to controlled roll-out documents and who can lean on account managers for information.
The front-line BT Retail staff don't have access to the same detail.
It's also why small ISPs can offer such great service relative to BT Retail, even when using BT Wholesale. ADSL24, AAISP and others provide a fantastic level of support using their commercial relationship with BT. There are other advantages to using BT Retail, but getting technical detail from Openreach is not one of them!