Jeanne,
I think I follow your line of reasoning.  I never practice making apertures seperately from blowing air through them, so I think I'm pretty much in agreement to a point.  I haven't had much success telling people to start with their lips closed and let the air blow them open.  This might work great for beginners who have no muscle conditioning, but it really can be confining in terms of starting notes gently.  As far a muscle tension from specific muscles, we're talking very personal stuff here that every one has to work out for themselves.  Of course some knowledge on the part of the teacher can save alot of time and make all the difference.  Unfortunately, teachers have to teach everyone else how to play, even if they have different physical characteristics.

Also, we have to use our ears to experiment with the balance between size of aperture, amount of lip tension required to maintain the aperture, intensity of air, and mouthpiece pressure.  Another very important point at the advanced levels is the shape of the aperture, which is where your comment about lip compression vs. roll in becomes useful.  Basically, if the aperture isn't getting shorter for higher notes, we are going to have to either use more lip tension or more mouthpiece pressure to get the high notes, or both.  This just doesn't sound good and is only effective for a few notes.  The size and shape of the lips as well as the mouthpiece determine how much roll in vs. how much lip compression will work best (shape of the aperture.)

Recently, I have tried to teach embouchure from the stand point that its function is to (along with the air column) create the appropriate size and shape aperture, with the appropriate amount of muscle contraction to maintain that aperture against the air.  This seems to help reduce excess tension, stretching, and just keep things simple, ie  BLOW AIR THROUGH A HOLE.  Oh yeah, we also have to wiggle our fingers and say da, but none of this should be cause for tension.

Sorry for the wordyness, it's a lot easier to demonstrate than to write about.
John Daniel
Prof. of trpt
Penn State Univ
 

PS  In working with an embouchure change student recently I had great results just forming an embouchure and blowing air through exactly like I would for each pitch and having the student imitate this gesture.  Each pitch took many attempts away from the horn,  Once the student started "blowing air through a hole" pretty close to the way I did, they were able to do this into the horn with pretty good results.  It really drove home the point that the physical gesture isn't difficult, but it is very precise.