Wedding Dress Sizes

I'm a little woman.  I am 5'3" and about 110-115 lbs (depending on the day!).  I wear a size 0 and rarely a 2 (depending on the manufacturer).  

However, I was a bit shocked when I went to get measured for my wedding dress.  The lady measuring me told me that I was a perfect size (which doesn't happen very often).  Yep, a perfect size 6.  How is that possible??  

I was told beforehand that I would most likely have a bigger size in my wedding dress than what I normally wear... so, I was expecting a 2 or maybe even a 4.  When she said 6, I'm sure my jaw probably dropped.  

I don't pay that much attention to sizes or numbers.  I love my body.  I like the curves I have and I'm happy with the way I look.  I just want to know where that number comes from!  How can I be a 0 regularly and a 6 on my wedding day?  

Shouldn't wedding dress designers want brides to feel thinner instead of making them feel larger?  I mean, a bride is supposed to feel gorgeous.  The number isn't very important to me, but what about for brides who are more sensitive about their weight/size?  I would think that making a huge size jump like that could be devastating to some!  

But, no matter the size, I know that I look awesome in my wedding dress.  :)