I worked at a gas bar over the summer (i'm a university student). We didn't charge for air but just to clear a few things up
-we made 3 cents on a bag of hostess chips
-3% or something on lotto sales (i was surprised by how low it was)
-we had the cheapest smokes in town (10 bucks), weren't making much profit on em, but people bought gum and stuff
-25 cents on a car wash (and if people complained about it not coming clean we gave em a rewash, byebye profits

)
-the air hose was stolen twice in a two week period, the hose was $20 or so to replace
-squeegee's were stolen regularly as well
-stations aren't making anymore than they used to on the ridiculous gas prices, yet we had to put up with people bitching to us how we were making so much money on it
-i'm pretty sure the owner didn't make any money at all on gas (although the corporation probably did)
-regular payouts for the canadian tire name
as others have said, the money is in the gum, coffee, etc...I'm not surprised some stations have started charging for air. What I am surprised about is the amount of complaining...I saw a news story and they interviewed somebody and she said the price was like 25 cents for 5 minutes or something? ITS A QUARTER!

Air is free, but air compressors aren't