Coming into the 2010 draft the Colts had 2 DEs coming off back to back Pro Bowl honors, while the Super Bowl had shown the need for a viable backup, Freeney had only just turned 30, while Mathis turned 29 (both in February). In addition Freeney's contract had another 3 years remaining with 2 left on Mathis' deal. DE was not what anyone would have called a frontline need.
Not that it was surprising the Colts passed up players at what was considered bigger "need positions" to take the best player on their board. Their history under Polian is filled with such moves, and Polian said in one of the mid-draft press conferences that Hughes was the only player remaining that they had given a 1st round grade. Hughes wasn't drafted because the Colts were unhappy with Freeney and/or Mathis, but if he lives up to his draft position (a pretty fair bet for a Polian 1st round pick, with the profile of a top edge rusher) it seems likely he'll push one of them out the door down the line.
Featuring 3 great pass rushing DEs is really only possible for a 4-3 D if one of them can play inside (a-la Justin Tuck) or at linebacker. Freeney, Mathis and Hughes are all undersized ends who do their best work attacking the edge, with little to no experience in coverage (Hughes has some, but there's been no indication he's even being considered to play SAM LB). When you look ahead to 2011 and 2012, the Colts will have to decide whether to extend or re-sign Robert Mathis when they have Freeney still under contract, and have Hughes signed for years to come. Barring Hughes busting or Freeney struggling with injuries, aging or underperformance it's hard to see a justification for paying the massive contract Mathis is well on his way to earning. Paying a 31 year old Pro Bowl end, Pro Bowl end money is a tough sell if you are already doing it on the other side and have someone you believe is a capable replacement making a relative pittance (while a rookie cap is very much needed, rookies outside the top 10-15 picks are quite affordable).
Just as Marlin Jackson worked as a role player for several years before graduating to a starters spot, Hughes can be expected to contribute (hopefully in as dramatic a fashion as Jackson did), before taking over for one of the starters he worked behind (hopefully with far better luck when it comes to injuries). There's just no room for 3 fully developed edge rushing DEs on the same team, and when decision time comes, Hughes will be young, cheap and still under contract for multiple years, while Mathis will be due for a mega-deal on the downside of 30.
So enjoy the couples years of phenomenal edge rushing we can expect to see from this trio, and remember to appreciate Mathis (and less likely, but possibly Freeney), while we still have them.