Most of them flow from SL4's specific focus on singularity issues. LW's "common interest of many causes" approach makes it so that:

• some people who used to read SL4 don't read LW, because they're not interested in most of what is discussed here
• singularity posts on LW need to spend more effort appealing to a wider audience
• singularity posts on LW need to spend more effort bridging inferential gaps

There are also subtler cultural differences that it's harder for me to put my finger on. I suspect the strangest-sounding true thing that could comfortably be said on SL4 was stranger-sounding than the strangest-sounding true thing that can comfortably be said on LW.

Of course, I don't mean to deny the huge advantages LW brings; the karma system works well, and a large audience is useful in many ways. But maybe there's a way to keep the best of both worlds.