/usr/share/texmf/xdvi/XDvi has the line XDvi*paper: a4 It should be changes to XDvi*paper: us (at least for the US version of RedHat).
BTW, bug report #492 states that this problem (wrong default paper size) was fixed for dvips, but does not say if it was fixed for xdvi.
I have verified this to be as ws reported and is being passed on to a developer for further review.
This change request has been made. No other files appear to have a4 paper sizes included in the config files.