The at-spi2-core component uses some GDK stuff, what makes it dependent on GTK+. This is a serious bug sine the at-spi2-core should be GTK+/Qt independent as far as I understand it.
This has been remedied in commit 0ab59218b5a070632bbc963
and a registry-daemon only dependent on X-lib is therefore available
in release 0.1.5.