If you're about to buy $82000 worth of anything, you don't generally toss it in a cart and push it around the store. Especially if it's going to take them 60 days to make the thing you're buying. Chances are you make a note of the details and contact a salesdroid. There's all sorts of stuff you need to work out with these people if you're going to buy a serious water sculpture. Where's it going and how's it being delivered and installed? Who's taking care of the design and construction of the pool and plumbing for it? Would the artist like to have a look at your site, listen to your ideas, and compose something special?
But "make a note of the details and contact a salesdroid" doesn't make a very good button label, and I'll even bet selecting a more natural or accurate metaphor wouldn't help, since it would become an unfamiliar online purchasing experience. Besides, it's useful to give the illusion that it's that simple to make a major purchase. For many luxury items, "nevermind, this looks like more trouble than it's worth" is the kiss of death. We all hate those sites that give no hint of price and only divulge the phone numbers of salesdroids.
Thus I'm forced to conclude that the "shopping cart" is occasionally supposed to be a metaphor not for the everyday real world situation where you push a real cart around, but for the everyday online purchasing situation where you use a "shopping cart" to keep track of items you haven't yet committed to buy. The appeal isn't "oh yeah, like in a grocery store", but rather "oh yeah, like at Amazon". Amazing.
What, you expected a point? Ok. I'm watching a metaphor being turned into a figure of speech. I like the way real objects can quietly slip out from under the ideas we build upon them, like the gold that used to back our currency. The stream of water keeps curving after it comes out of the crescent, but no longer because of the crescent.