As recent events have demonstrated, the US firmly maintains policy ambiguity in its relationship with Taiwan. Under the joint communiques the US "does not challenge" China's claim that Taiwan is a part of the People's Republic of China (PRC). Much later it also has stated that the US does not support Taiwan independence, and now it seems to be interpreting its recent new ambiguity -- "not supporting any move toward independence" (as that is defined by the US, presumably).
At the same time, there must be no unilateral change to the status quo and there must be a peaceful resolution of the cross-strait issue. Change inevitably is making the former demand ring rather hollow. While the US presses China to enter into dialogue with Taiwan -- a positive effort -- another dialogue is badly needed as well.
The statements made in Beijing by US Secretary of State Colin Powell followed a pattern used by US President George W. Bush in his press conference in Washington on Dec. 9 last year just after talking with the Chinese premier. In both cases, some of the wording used by the US was very much like those used by the PRC. This might explain some of the wording if both of them were "winging it" (not using their briefing notes).
This problem, by coincidence or not, has happened at a particularly vulnerable period for Taiwan. Almost as important as the US presidential election is the fact that Congress is not in session, since its own election takes place at the same time. Conventional wisdom is that at such a time, little can be done as the principles are occupied elsewhere. But it can also be a time when changes clothed in the appearance of continuity can go by unnoticed.
The international as well as the local media in Taiwan has been speculating on the motivations behind the statements made by the recently. It would take a page to name them all. I will add a few more mundane thoughts: leaders, and sometime their aides, often seem to have an urge to explain a continuing policy but use different words to do so -- it gives them more face than repeating someone else's words.
Recently, there is a habit of having a press conference right after a meeting with a high-level host or visitor, with only a few minutes, if any time at all, with aides before meeting with the media.
But fundamentally, what this demonstrates is the downside of ambiguity. Ambiguity is an important and useful means of maintaining flexibility while getting around a difficult issue. Diplomats in particular can't live without it. But it also leaves a commitment open to different interpretations.
Though one can raise many examples that were good or bad for either side of an issue, two that have been very harmful to Taiwan were the "no support for Taiwan independence," and now a comment on Taiwan's sovereignty. Both comments can be interpreted as no change in US policy, but both disproportionally harm Taiwan. And both effect commitments made by the US. It could also be said this is moving toward "no independence."
One example is the clear policy enunciated in the April testimony before Congress on US policy toward Taiwan. The US defined its fundamental stand that the status quo must be maintained; that there should be no unilateral change to it by either side; and that there must be a peaceful resolution to the differences between the two sides of the Taiwan Strait.