I found a nice article over at guardian.co.uk with some more details about the Shouwang Church.
First of all, it gives a little more detail about what sets Shouwang apart from other churches. Shouwang is what is known as a “house church” which means that it operates outside of the government established and recognized Protestant and Catholic churches. These “house churches” have more Evangelical leanings, and meet in their own spaces (or whatever spaces they can find that are available), homes, conference rooms, etc. According to the Guardian article, one of the main draws of these over the mainstream churches is their independence from politics, which are apparently major part of the state-run churches. No surprise there.
These two distinct categories of church also explain the disparity between official estimations of the number of Christians in China and independent ones. Official estimates are, of course, based on the official churches, whereas the independent estimates try to take into account all of those who call themselves Christians, including members of these house churches.
The article also clarifies that it was leaders from these house churches who signed the petition to the Chinese government, and goes on to say that this is the first time that these groups have really stood up for themselves. Unsurprisingly, this has some of them worried. The leaders of these small organizations have been taking measures for years to make sure they do not strongly offend the government, even though their meetings are technically illegal, and even in the petition, the leaders made sure to reassure the government that they are still loyal Chinese citizens, just ones with an interest in perusing their religion on their own terms.