Sony's can also capture the page as an image with scribbles intact but they are not saved in the body of the actual pdf viewable with any other PDF reader on another platform like windows. They are using PDF viewers not editors that have annotation capability.
I did find one actually that does work in linux
http://www.qoppa.com/pdfstudio/index.html i have no way to try it here but ill give it a shot on a friends ubuntu machine when i have a chance. I don't know if it could be ported for readers , or if they woudl be interested.
The GNU PDF project
http://www.gnupdf.org/Main_Page is where the main push is happening for free tools being developed for fully functioning PDF support in linux