Actually, this is simply not correct. It is, however, an unfortunate and not altogether uncommon misunderstanding. There is NO 'PADI standard' such as you suggest, in this case.
1. PADI General Standards and Procedures do specify that 'standard diver equipment' includes a 'Primary regulator and alternate air source'. The term 'octopus' is not used, nor are hose lengths specified. PADI 'Standard diver equipment' can just as easily include a primary second stage on a 7' hose, and an alternate second stage on a 28" hose, with a bungee necklace, as it could include a primary second stage on a 36" hose, and an alternate second stage on a 40" hose. Or, it could include a primary second stage on a 40" hose, and an alternate second stage on a 36" hose, with a bungee necklace.
2. For air sharing in an OOA situation, PADI language does NOT specify which second stage is donated to the OOA diver. The terminology is: a) for the donor - 'Supply air to another diver using an alternate air source', and b) for the recipient - 'securing and breathing from an alternate air source supplied by a buddy'. The word 'alternate' refers to something that is an alternate the OOA diver's equipment, and is NOT restricted to the donor's 'alternate air source'. The supplied air source could be the donor's primary, the donor's alternate, a regulator from a pony bottle, etc. If I donate my primary second stage - what is in my mouth - to an OOA diver, and change to my alternate air source for my own use, I am fully compliant with all PADI standards.Now, it is not uncommon for dive shops, be they affiliated with PADI, SSI, SDI, NAUI, whatever, to teach using the approach you suggest - the donor gives their alternate air source, often on a 40" hose, to an OOA diver. That is simply a reflection of (primarily) history and habit, as well as the lack of familiarity, of some shops and instructors, with other equipment configurations. They may be the 'best instructors' in the area, but they may not have experience with alternate configurations, or the instructors may be constrained by shop practices, and available equipment So, if you are planning to pursue a configuration that would include a long hose / bungeed necklace configuration (which I advocate as a general practice), or which involves 'primary donate' as the preferred approach in an OOA situation I would look for a shop - and instructors - that would be comfortable, and familiar with, the configuration you plan to use. If a shop tells you that 'octopus and in an OOA you give or your buddy takes the octo' is a PADI standard, you may wish to reconsider whether you wish to be re-certified through them - that is not a PADI standard, even if it is a shop default.It certainly should not be, for a competent shop. You should not have issues diving, on trips or locally, with a shop that says you cannot dive with what you describe as a DIR or Hogarthian configuration. However, if a shop were to say that such a configuration would be a problem, I would suggest you reconsider diving with them and look elsewhere.