The right starting date is 1993. Because that is when the first commercial online site came online. However that company got sold to AOL in 1995. See http://en.wikipedia.org/wiki/Global_Network_Navigator for details.
The second company to try to make money on the web was Netscape. It was founded in 1994, however its IPO was in 1995. So that is two reasons why 1995 is important at the beginning of online commerce.
I'm curious what caused them to choose 1995 as the birth of online commerce. It wasn't paypal's founding. That was in 98.