The problem I'm talking about is not specific to KDE. KDM simply uses the auto-detected resolution which is always wrong if I don't have an xorg.conf.
I can live with it since I don't re-log very often and I haven't motivated myself to write the xorg.conf yet. On the one system I have that's running Gnome though I couldn't figure out how to set the resolution (it comes with what seems to be a preconfigured list of useless options) so there I did have to resort to writing an xorg.conf.
Note that at least one machine detected the resolution correctly on 2.6.32, but no kernels I've tried before or since.
I haven't tried any kernel versions that are particularly recent since the rate of regressions in Linux has conditioned me to upgrade only when it's completely unavoidable.
(And as for monitor *hotplugging* in KDE...that's a pretty guaranteed way to render this laptop non-responsive and require a power cycle)