Yes, the heuristics in xserver-xorg.postinst.in are approximate at best, and make a number of rather ambitious assumptions. These often work correctly, but sometimes result in bugs such as those reported.
Anecdotal evidence suggests that xorg itself (with no xorg.conf) can do a better job of detection in these circumstances, however this remains to be tested.
Yes, the heuristics in xserver- xorg.postinst. in are approximate at best, and make a number of rather ambitious assumptions. These often work correctly, but sometimes result in bugs such as those reported.
Anecdotal evidence suggests that xorg itself (with no xorg.conf) can do a better job of detection in these circumstances, however this remains to be tested.