I think it's a question of Uber's role in the transaction, and whether they're considered an "Agent" of the seller (the driver), or the transaction's principal.

I think this is a matter of accounting judgment.

I'm not an accountant, but I remember reading somewhere that pure agency transactions have different accounting treatment vs. "principal" transactions where the party in question assumes more risk and is not acting strictly as a representative of another party (the UberX driver).

[1] http://www.journalofaccountancy.com/news/2015/aug/fasb-propo...