So if I'm already looking at the webpage, why bother driving to the store to get it when I can just click "buy" and be done with it? The only reason I'd bother with driving there in person is if I really really really need it fast.

And as the other responder said, those inventory counts might not be accurate; if there's only one in stock, and someone just bought it 10 minutes ago, is the webpage really updated that fast?