you can usually be sure that footage captured from a consumer DV camera through firewire is lowerfield first. I’ve found most professional NLE’s are upper (I don’t know why). If you search the archives you will find a way to determine if footage is captured upper or lower, I just can’t remember the process at the moment.
My guess (and I’m not really sure of this) with tape machines, is that there is no dominate field order until it is captured. The tape machine just plays all the fields in the order they are on tape…..it’s when you capture those fields (half frames) and want to work with them as full frames that it becomes an issue. hmmmmm, it makes sense in my head….