Quote - i don't own an i-phone or a tablet, and i would like to understand something about these modes of web usage vis a vis a web site such as Rosity.  are people who use these instruments actually able to purchase and download with them, or are they just able to browse and perhaps view/comment in galleries/forums? 

Yes, it is possible to purchase via an iPhone/tablet. The web site is displayed in a browser just like on a desktop/laptop with the same functionality. However, if I purchase via my iPad I always download the zip files to my normal computer later.