I don't know the price of brand-name replacement batteries in the USA, but the price didn't surprise me. It's comparable to replacement batteries from Telus/Bell/Rogers stores and smart consumers avoid non-brand, cheap replacements.
As for the consumer association rant in the link Hugh posted - it was mostly an attempt by the association to get in the news. I doubt many early iPhone purchasers were surprised that the battery could only be replaced by Apple, or that they cared. Apple fans have known for six months that the battery would be like the iPod battery and require Apple replacement. It's part of the price of being a "Mac person"
As for why iPod and iPhone batteries require a trip back to the Apple shop for replacement, I suppose it has to do with keeping the design sleek, smooth and thin. An iPod with a battery cover and latch just wouldn't be quite the same.