I run a coffee roasting operation and do some consulting for other coffee firms so I can tell you that in a lot of cases it isn't. What are the costs here? There's the cost of Internet access, which the business would have been paying anyway because they're using it to order from some suppliers, check bank account balances, and so on. There's the cost of a wireless router, but that's a pretty cheap one time cost that amortizes to 0. There's the cost of the electricity needed to run the router, but if that's significant on a per-cup-of-coffee basis that shop has bigger problems than wifi moochers.
The trade journals have been covering this trend for a while, but wifi is really just a convenient scapegoat for the real problem of a lack of customer engagement on the part of staff. While wifi might bring in a different demographic of moocher, this isn't really a new problem. Some years back I went into another coffee shop, ordered my single espresso, a large coffee, and some food, then found no indoor seating available at all. The seating area had been completely taken over by students. You'd see even at the largest tables, one student with their stuff spread all over it. I was later in a meeting with the owner of that shop and I told him about this. I also told him about my customers who also like to take over a big table and spread things out, but when the place gets busy, they pack up and move to a smaller table. He was impressed as his customers never thought to do that. This was a place that didn't offer wifi at the time, but it was the same problem with the same solution. Get to know your customers and when seating starts getting scarce, get out from behind the bar and suggest to the person using the largest table that he could move to a smaller table so the family of 4 that just came in can sit together, introduce customers to each other and ask if they'd mind sharing a table, things like that.
My policy on wifi is the same as when I put it in (and customers know this policy). It's free, it's open, but if it starts causing problems I'll get rid of it. So far it's been beneficial. Customers who spend a lot of time in the shop (but keep buying things while they're there) are there longer (and buying more) because they no longer have to run home just to check email. It's brought in more customers. It's also made it easier for me to make certain workflows data-aware (for example, the computer in the roasting area communicating with a database keeps inventory figures current and makes the roasting log both more detailed and easier to use, see my homepage for more details) without running ugly cables all over the place. That said, the coffee market in many major American cities is such that some independent shops can afford to pick their customers and if your customers think you have the best coffee in town, they'll be willing to deal with the minor inconvenience of lacking access, or rather, instead of laptops, they'll be on their cell phones. Personally, I'd rather have the laptops, but then again, my customers talk to each other.