Not sure whether my iPad is the only one that does this, but reading the post above makes me wonder.
I am away from home for a week at a time. During that week, I stay in a couple of hotels that have wifi hotspots, and hang out in a couple more places that also have them. My iPad and iPhone pick up the wifi immediately in every case, and when i return home, I'm back on my home network until I leave again. I have never had to input a known password twice.
Just sayin'. Maybe there are other factors to be considered here?