I think iWork on the web will have the same functionality as the paid apps on iOS (as far as technically feasible i.e. similar to how iOS iWork apps lack some features of their Mac OS X counterparts). AFAIK Apple doesn't have a history of offering free and paid tiers for the same app.
Furthermore, since new iOS devices now get iWork apps free, it's likely that new Macs will also get the next version of iWork for Mac for free.
A free, powerful office suite on iPhone, iPad, Mac & Web seamlessly kept in sync via iCloud would be pretty cool.