In practice, their official policy lets Taiwan exist as an independently governed region more than the US even allows Hawaii or Cuba to be independent. Even Canada has more of a attachment to the US and its laws than Taiwan does.
This is probably a fact lost on most foreigners unaware of the situation.
If China really wanted to assimilate Taiwan they would not have such deeply connected bilateral trade, cross-border tourism, or give access to their market by Taiwanese companies like Foxconn, HTC, Asus, and hundreds more.
China does impose tourism restrictions to pressure Taiwan, but if they really wanted to crush Taiwan they can easily do so without raising so much as a hand gun.
The funny thing is armchair Chinese nationalists (people on the other side of the planet reading hacker news) are more up in arms about this than actual Taiwanese people because the de-jure stance has always been like this, and the de-facto independence of Taiwan has been pretty stable.