Yeah, but if you are trying to automate thousands of simultaneous requests, you'll have to use a lot of servers, which is costly even in the cloud.

Right now google and bing will run sites with JS enabled to see the DOM after any JS changes take hold. Usually these crawls aren't nearly as often as the general crawling, because there is quite a lot more CPU/Memory overhead to such utilities. I can't speak for splinter, but similar tools in node or phantomjs have a lot over overhead to them.