Depends on what they were....if they were 7200.11's, I'd say you were lucky they lasted this long as that model is several years old and had a well known firmware defect. If they were 7200.12's and died so close to one another, I'd say it's too "coincidental" not to investigate a possible common cause.
The 7200.11's have been reported to have the highest failure rate among drives in recent months....it still catches buyers as they are most often sold along 7200.12's at heavily discounted prices. These problems were not however common to the 7200.10's or the 7200.12's ....
If ya check the reliability database over at storage reviews.com you will see just about every manufacturer has had a 'dud' model now and then....IBM had the infamous Deskstar failures in one model and one of the WD raptor models had a 25% failure rate. As each manufacturer has had their turn at having a dud, it' important to focus less on vendor than on model.