By the way...Signature Debit is also known as "offline" debit whereas PIN Debit has been forever called "online debit."
That being the case, why do YOU think "online shopping" doesn't offer "online debit?" Watch the video...it's chock full of "Fees Frames"
Visa Reigns with Silent Tax
The growing use of debit cards has meant big profits for Visa, and there are concerns that the company's market power has led to unnecessarily high fees to merchants.
Fees Frame... http://video.nytimes.com/video/2010/01/04/your-money/credit-and-debit-cards/1247466238575/visa-reigns-with-silent-tax.html