For the 1-3% fee businesses, it does actually make sense. Especially with really low-margin sites. Think of your local grocery store offering a cash discount because of credit card fees, those businesses really do exist on the margin.
Both the minimum order and extra international shipping costs will go away as we move forward. They were unfortunate hurdles we had to place in order to get the site public on schedule.
We're adding the option soon. For now we just wanted to get the site out there so people could see the savings they can receive if they use Bitcoin. Having the prices set in USD helps consumers compare across sites much easier.
Products vary in pricing. We don't undercut them on every product, but the fact that we're able to undercut them severely on a good percentage of our products is amazing!
The advantage to using Bitcoin is that there are no payment processing fees. What we're able to cut with BitcoinStore is that 1-10% fee that Visa, PayPal, et al. charge especially when dealing with products that have a high chargeback risks. So the products that sell best when using Bitcoin have high chargeback risks associated with them.