Yup, that's exactly what happens. One push focuses. Another push snaps the shutter. But you have to be quick. If you don't press it a second time right away, it will just refocus. Like a double click.
And for the record, the USB remote absolutely will work with the SX10is. I have one, and it works fine on 4.5 volts. I built the remote from a project box, switch and 3 AAA battey holder from Radio Shack. It's sort of my proof of concept. I'm going to build a smaller more ergonomic one that uses watch batteries just as soon as I have time.