The BBC use the platform neutrality rules as and when suits their motives. They've let BT Vision have the iPlayer even though subscribers would be restricted to BT Broadband, and I assume Virgin Media customers all get their internet through Virgin too.
Which is why in this case its got less to do with 'platform neutrality' and a lot to do with branding and making sure people realise they're accessing a BBC service, even if it is via Sky.
There are a number of factors that dictate which platforms the BBC will develop / offer iPlayer too- the number of people using that platform, how the platform owner wants to present it (including the user experience and the technical issues (could be DRM, coding, way the content is served up).
They haven't been against it being accessed via an ISPs broadband but they have been unhappy about it being part of an additional subscription - which is why it wasn't on BT Vision for a while and - I believe - was removed from the Xbox 360. Paying for access to a platform its offered on is one thing, making it part of an additional subscription is quite another. They've now got a situation where is widely available- on platforms where you pay upfront (games consoles, phones), others where its included as part of a service you subscribe to access (BT Vision, Virgin, soon to be Sky) - but not part of an additional charged package.
And before you start off again on the BBC and 'platform neutrality' the cutting back of the red button services on satellite is about costs above anything else. It now means they can have one less transponder - saving several £m a year - and the future of such services is via IP, so it makes a lot of sense. That's been pointed out to you a number of times but you still seem to feel you're hard done by because the BBC has had to save money and are cooking up some conspiracy theory when the main motivation is pretty clear.