I've been using Pandora for years. I didn't even know that there were preset stations! I create my own. Thats kinda the whole point. It might be that you can't create your own stations w/ the android and/or iPhone app? I've got and use the iPhone app, but I created my stations a long time ago online, so I never tried from within the app. If you can't do it over the phone app, log into their website w/ a pc and do it.
For example, for one station I just put in the artist Steve Vai and I caled it Vai Radio. The first song will be a Vaqi song, and then it will be stuff somewhat like Vai (Gary Hoey, Satch, Greg Howe, Michael Lee Firkins, Andy Timmons, etc.). I have created for myself (among others) Vai radio, Mahavishnu Orchestra radio, Megadeth Radio, Pantera Radio, Django Reinhardt Radio, Ry Cooder Radio, Blind Blake radio, Robert Johnson Radio, etc. You just put in an artist and it does the rest.