Google had the significant advantage of starting when the internet was relatively small. They had fewer users and likely low bandwidth costs. Twitter doesn't have that advantage, if it takes twitter and identical amount of time to figure out how to make money as it did google, then Twitter could likely be in so much debt they go bankrupt.
They're taking equity financing, not debt. Equity doesn't have to be paid back (well, presumably the investors want dividends or an exit, but they can't force the company into bankruptcy if they don't get it).
If you figure 33 employees @ $200K/year, they're only burning $6-7M/year. With $55M in cash, that's like an 8 year runway. Granted, they're not going to stay at their current size forever, but they hopefully won't stay at their current (lack of) revenue forever either.
