digital items are bought an awful lot. They can be used on websites, in website designs, they could be artwork that can be printed on whatever format the customer wants, though those are usually more than $2.
Because they're so cheap, they arrive so fast, are not a problem to replace if the email gets blocked or lost and would serve the customer no purpose if they lied to get more, people buy them a LOT. People are also more inclined to buy more in one purchase. I've only purchased digital items once. I stumbled across their shop, saw the $3 price, and ended up browsing because my pocket allowed it, and ended up purchasing 3 pieces. No, it's not a huge number, but I bought them without the need of them, just because I liked them, and because they may well come in handy in the future (this was a few months ago, and I ended up using one as my blog background).
So $2 may not seem much, but it's uncommon for people to buy one piece from them anyway. I have a couple of friends who have digital shops that sell tiny priced things and more expensive things, too, and the cheaper things make them just as much money as the pricier things.
It's a sound business choice for the longrun, but only if they can get a lot of people's attention, and they have a very wide selection.