Agreed that keeping Carter was part of it.  But I think it goes deeper than that.  I think they wanted to start getting some youth into that starting secondary while they had the chance rather than waiting too long for them all to get old about the same time.

It also creates more long-term consistency in the secondary to replace Ward now.  Talib is probably next in a year or two.  You want to spread those replacements out a year or two apart if possible to minimize the disruption.

Bottom line, I think it was more about getting Simmons into the starting lineup than anything else.