I agree. It's not new, and it's not specific to us.Across all of college football, generally only half the players in a recruiting class become major contributors. The 2013 class is no different. If the other guys weren't fits for the program, better to get them out so we can bring in fresh blood. Those guys are no longer in the program for a reason.
After a 5 minute Internet search, here are some interesting links I found.
1) The OP walks through simple math to calculate the minimal attrition rate that must occur, in order for schools to be at 85 scholarships (total) each year:
http://auburn.247sports.com/Board/42/Contents/Attrition-in-college-football-8345188
2) Article from Chicago tribune, which focuses on the 2008 class of Illinois state (17/22 left before graduating), but mentions many of the reasons why recruits leave programs.
http://articles.chicagotribune.com/...all-players-college-football-graduation-rates
3) Fascinating article from a higher Ed source (somewhat OT, but peripherally relevant), talking about graduation rates and how they can mislead, advocating for an "adjusted graduation gap" rather than the "graduation success rate", or GSR, which is what's favored by the NCAA:
"Enter the Adjusted Graduation Gap, a model that compares athletes’ graduation rates by conference and sport directly to the rates of their non-athlete peers by factoring out part-time students."
https://www.insidehighered.com/news...-graduate-rates-lower-full-time-student-peers
4) this one addresses the question posed by the OP directly. Some dedicated soul calculated the attrition rates for all power-5 programs since 2002!! Bottom line - Iowa's attrition rate slightly higher than the average B1G attrition rate.
Over a 12 year period, the overall attrition rate for the entire B1G was 37%. Iowa's, during this period, was 40%. Indiana's was the highest (44%) and northwestern's was the lowest (24%).
https://www.reddit.com/r/CFB/comments/2y4waq/power_5_conference_attrition_rates_for_2002/