xfsdump vs tar

[Dan Swartzendruber <dswartz@xxxxxxxxxx>]

The common wisdom is that dump is dangerous to run on mounted 
filesystems.  I do so for weekly backups
on my home system, because it is scheduled for 2AM on Sunday morning, when 
things are relatively idle.
I note from the man pages that xfsdump can only be run (apparently) on 
mounted filesystems.  Is there
anything fundamentally different about the implementation of xfsdump (for 
linux specifically) as opposed to the
other dump programs (such as for ext2 filesystems) that makes this "safer"?