But how Uber could benefit from answering this fishing expedition? If I were Uber I'd simply stonewall. They are under no legal compunction to answer, and virtually no answer would help them.
Here's a nice white paper on Congress's subpoena power: http://www.mayerbrown.com/files/Publication/ec1203b2-a787-44...
"The Enforcement Process. Congressional investigations often begin informally, with the interested committee or subcommittee first seeking information on a voluntary basis (i.e., by sending a letter request or asking for an informal interview), rather than by issuing compulsory subpoenas. Although there is no legal obligation that a party comply with such a request, it is typically in the responding party’s best interest to do so"
The federal government can make your life extremely difficult, fully funded startup or not.
Profitability has a lot to do with how you spend your money. "Startup" is commonly used to connote a small, new business. The dictionary says it is a "fledgling" business.
If Uber's revenue were the GDP of a nation, it would have 40 countries ranked below it. That's not a "fledgling" business, even if it isn't profitable.
It's an opportunity to establish publicly that your company won't be engaging in any of the kind of shenanigans that can cost you customers in a competitive industry.