This could actually be a feature added in OS2008, specifically with the N810 in mind - as it has only a single card slot it would be quite important. On the N800 w/OS2007 there didn't seem to be such a feature - at least there used to be lots of reports about only the external slot visible. It all turned out to be because those users had VM enbled on the internal card. It makes sense to automatically (when possible) turn off swap when the USB cable is attached.