The version of the spread that ISU has been running for the past three years doesn't keep defenses from cheating up or putting more players in the box. In fact, if anything, it encourages defenses to cheat up (which is pretty much what Rutgers did).
ISU's "spread" doesn't spread the field vertically. Pretty much all the routes are run within 15 yds of the line of scrimmage. ISU rarely runs deep routes. Defenses know this, and they congest the area where the routes are run, which makes it difficult to complete passes and establish the run.
Until ISU spreads the field vertically, the spread offense will struggle. It's a chicken-and-egg thing. The defense will not respect the deep routes if the QB/WR combination doesn't provide a credible threat of completing the pass, but the QB/WR combo won't get the experience to make the completion until they run are given the opportunity to throw/catch the deep passes.
Somehow, ISU has to develop a credible (doesn't have to be outsanding) deep threat, or the spread will always struggle.
Part of that is the style of defense used in this league. Against press coverage vs 2010 TTU you guys went deep with regularity. This year there was less sense in throwing deep routes as quarters, three deep zone, and other "keep them in front of us" tactics were employed by pretty much all but UT. Add to that inconsistent QB play and it is even less of an attractive proposition. I know you guys got us on one or two deep ones so the scheme uses them but whether it is opponent schemes or little faith in raw QBs they were not called on as much.