We love a great bridesmaid dress and found a website that explained the tradition (www.howstuffworks.com).
"While it may feel like cruel and unusual punishment for several women to show up to the same event expected to wear the same dress -- not only in the same color but in the same style -- there's a reason behind the tradition. Or, at least, there's a superstition that started this whole matching thing.
If you've never been able to reuse a bridesmaid dress, you're not alone, but the wedding tradition didn't take hold to make you look bad (and the bride even better). Really. Instead of blaming the bride, blame the Romans. Because of Roman superstition, Roman law required 10 wedding guests to dress similarly to the bride and groom (groomsmen, your matching tuxes also fit here) for good luck -- the matching outfits were thought to confuse any evil spirits who might want to curse the couple [source: Gordon]."