Because I don't know a lot about garbage collectors, but I am familiar with Mikes amazing work on LuaJIT and I trust that he knows enough about what he's talking about (based on the quality of his luajit work) for enough of his claims to be true for this to be interesting, useful or both.
The thing you have to understand about Mike's work on the new LuaJIT GC design is that it's heavily constrained by the Lua API. It's not a very interesting GC, though it does improve slightly on the standard tricolor incremental marking GC. See my reply to your other post.
Because I don't know a lot about garbage collectors, but I am familiar with Mikes amazing work on LuaJIT and I trust that he knows enough about what he's talking about (based on the quality of his luajit work) for enough of his claims to be true for this to be interesting, useful or both.