"Bastian Blank – which is the person (among others, but mainly him) that is packaging Xen in Debian -, has decided last summer that he doesn’t want to deal with the qemu-dm of Xen, thus removing Xen Qemu and support for HVM in Debian.
Before anyone flames Bastian Blank, I’d like to highlight the fact that maintaining a PV dom0 in a distribution needs quite some work, he does it for free, and that he should be thanks for his work within Debian, rather than being blame for his maintainers choice."

Source: Debian-News