sometimes you simply get unlucky, unfortunately. Many more failures however, and I'd start to take a look at your environment. Your failure rate definitely falls outside of the curve a tad
In a hosting operation, we have thousands of Seagate drives in production. We also have thousands of Maxtor drives previously deployed in production before our wholesale switch to Seagate. Maxtor has a somewhat higher historical failure rate than our Seagate drives in production - but in the end it's pretty close. The factor in choosing Seagate (before the maxtor was bought) was due to both the 5 year warranty vs. 1 year, and the fact that Seagate tended to be on the upper end of the performance and technology curve.
Seagate has been great in our book, lower than "average" failure rate, and RMA procedures that are simple to do bulk returns with. Hard drives should always be treated as something that is about to fail - as that is exactly what they are.
I also strongly urge keeping a spare disk around for your array
A drive is much more likely to fail during the rebuild process, as that is when they are the most stressed. When you get into 15+ disk arrays, you start to see interesting mathematical probability issues - such as uncorrectable error rate per million sector reads. Doing the math someday can be a pretty wide eye opener.
Ah well, good luck!