The Sauce labs guys assume you have already recorded the script. With go-test.it you have a firefox extension that does the recording and uploading of scripts. Jason Huggins doesn't have a good opinion about recorders/IDEs. Selenium is very developer focussed (As JH himself said at one of his talks),but most testers don't code. Go-test.it seems to be based on Selenium and focussed on the average tester. I know for a fact that there are large companies that are willing to pay for this kind of product.

Update #1: Saucelabs records the video of tests which go-test.it currently doesn't seem to do.

seems not far off, but a hosted paid for version of the same thing. It's a lot easier to set this up than Selenium from what I've seen. Even if ease of setup is the only difference they'll still be a really popular service.