OpenBSD's a notable exception for ThinkPads specifically, primarily because most (if not all) of the OpenBSD devs do their development from within OpenBSD itself (i.e. using OpenBSD either as their primary system or otherwise with significant regularity), and said devs tend to reach for ThinkPads. So, naturally, ThinkPads ended up being the de facto "preferred" devices for (i386/amd64) OpenBSD.