A common theme in this thread is 'putting more oxygen in the soil with ripping/zone-building/etc.'  Chad H thinks his soybeans look better where this tillage occurred.

Tillage exposes the organic matter in previously stable aggregates to this oxygen flux.  Rapid decomposition ensues.  This releases N, P, K, S, Ca, Mg, Zn, Cu, Mn, Cl, and a few others.  What makes everyone so sure they don't have 'hidden' deficiencies of one or more of these nutrients?  (To further confound the situation, some of the zone-building and strip-till programs are putting down some fertilizers.)  Be careful what conclusions you draw!

As for tillage improving the rooting through hardpans, etc., again, the evidence is darned sketchy.  One can probably make the case for it before beginning a true no-till program, to rearrange some of the compaction layers from previous tillage (note that I said rearrange, not remove).  Thereafter, on prairie soils, I do not know of any mechanisms causing hardpans or distinct compaction layers at depth.  Tillage (zone-building, strip-till, paraplowing, etc) will only screw up the structure you have build up till then.