If you look at the old texts on judo, like the Kodokan book or the Canon or Daigo's book, seoinage is considered a hand throw, not a hip throw, meaning that the hand action is of primary interest in the the technique. Most folks though, teach seoinage as a large hip throw (what I call a 'crack of the butt throw' because you put the crack of your butt on their thigh as a fulcrum). Check out this video of Mike Swain's seoinage. I certainly can't gripe about his form, it is a beautiful, powerful, flowing hip throw, but it is pretty obviously a crack of the butt throw. Notice he specifically mentions overturning the feet to get more power - that positioning of the feet makes his buttcrack line up better with uke's thigh. Thus a crack of the butt throw.
...and here is the Nagenokata form - pure hand throw. Not only is there no buttcrack on the front thigh, there is almost no hip at all. The very side or corner of tori's hip might brush uke's front thigh on the way by but it's pretty obvious that there's no fulcrum at the hip - thus a hand throw instead of a hip throw.
The question - can we get the hand throw version of this thing to work in randori against a resistive opponent or do we just give up the ideal and allow seoinage to become a crack of the butt hip throw because this form is faster and easier to teach beginners?
- Check out Colin's post, about a hip throw in the Dosan kata, for a TKD perspective on this throw.