First, I would like to say that the Colts have won for so long because they know how to pick players. For instance, everyone is concerned about who will be the colts second running back. Honestly, do you think that the Colts don’t have a plan? Now a team like the Bengals, their draft pick, Kenny Irons, went down. Do you think that they have a decent backup plan? NO! Since Tony Dungy and Bill Polian have been in the league, they have won period. Don't worry about the Colts.
Second, everybody is worried about the Colts loosing decent players. However, the Colts defense was basically horrible last year. It really can’t get much worse that what it was last year. Everything that I have heard indicates that the new starters are better than the ones they had last year.
Third, kickoff and punt coverage were horrible last year. I am pretty sure both were the worst in the league. I can’t promise that they were dead last last year because I can’t get NFL.com to spit out the stats I want.
Finally, The Colts know how to find players, and when you are dead last in several categories, you don’t need premier, big-name guys to make a big difference on your team when you are really bad in an area. The Colts already have big names signed to their roster, they just need role players who can play backup receiver, corner, or tight end who can also play special teams.
As a little post script: I expect this to be one of the better defensive years for the Colts. Primarily because the Colts have some punishing hitters on defense. Keiaho, who replaced Cato June, hits way harder and is a sure tackler. Not to mention, the secondary is probably the best tackling secondary in football anyway.
I know that the D-line is suspect, but they have brought in some 300 lb tackles in Johnson and Pitcock. Johnson is a great pass rusher and I am sure that both will be more effective against the run than last-year's group. However, lets not forget that the Colts played without substitutes at defensive tackle for a number of games.