FYI, here's Tim Bray's explanation of the reasoning for that:
The only characters that XML dislikes are ASCII C0 control characters such as form-feed, vertical-tab, and those wonderful things like EOT and DLE and NAK and SYN, which have exactly zero shared semantics from system to system; which is exactly why they're not in XML.
Update: just to be clear, I am not supporting the argument — nor rejecting it. My only actual experience is limited to systems with very little variation: Unix vs Windows on the same hardware platform. I haven't even worked on MacOS X. So I don't know enough to make any argument here.
Makeshifts last the longest.