one of my colleagues and super-star-wizard-man david chou posted recently on platforms.
he previously was chatting about popfly as a platform and then thought it a bit more to back up from a larger view to help us ponder what exactly a 'web platform stack' means. i think for people who haven't really distilled it down into any consumable thought areas, it does a good job defining where some web platforms fall in to the greater scheme of the overall goals of a web strategy.
maybe i'm not saying it well :-) -- but you should go check out david's post about it and leave your thoughts.