[derefr]

Don't feel bad about not giving them money—they need to be free to read to sustain the level of net-positive impulse-edits they get (similar to how chewing gum needs to be at the checkouts of grocery stores to sustain its level of purchase.) Encouraging Wikipedia's free use, as a side-effect, makes more people likely to edit it, and thus makes it more valuable.

[jrockway]

chewing gum needs to be at the checkouts of grocery stores to sustain its level of purchase

I don't chew gum anymore, but when I did, I always got it from the chewing gum aisle. It's cheaper there. I'm sure I'm not the only one who figured this out.

[derefr]

I don't know how your grocers work, but mine just scan the UPC that comes as part of the product's packaging—and that's the same no matter which aisle you picked it up in. (You could just as easily bring something in you bought outside the store and "buy" it again.) Or do you just mean that the aisle section has larger bulk versions of the same gums?

[jrockway]

Different UPC numbers for the same thing. Yup, really.