When you're spending money like there is no tomorrow and you still have to really find your business model I don't think that qualifies as being in a state where you don't need external cash. Twitter needs it worse than a junkie needs a fix, without external money flowing in they would probably not last another 6 months.

Twitter is growing significantly and will continue to grow in order to reach mainstream usage, but that requires expanding their infrastructure and hiring more employees - hard to do without additional funding.