Just admit that you don't know anything about accounting.
I'll give you a free lesson: Sony and MSFT count shipped units in exactly the same way, because if they not - they will go to the court for tax fraud.
And stop listening to what people say, even if it's some funny executive. Just look at the numbers.
It has nothing to do with accountency, it's about giving numbers at different level of the production/storage/selling chain.
It's purely about marketing, and indeed, you can either use figures of consoles sold just when they exit production chain (and still have to be delivered to sotck before being dispatched to retailers) or at the moment their are dispatched. Damn, you could even be including number of pre-paid but not yet made units, if the practive was usual in this market (which is not, unlike the exotic car market for instance).
Don't know if MS is right about Sony, but indeed, it would be strange that Sony do not react if it was a lie, especially given the "marketing war" going on.