You missed the point. This is not intended to be a general browser. It has an enormous potential as an embedded browser in desktop app. iTunes is such an app, one that ships with its own modified WebKit. Things like Fluid [1] and Prism [2] allows you to quickly generate such desktop application using Safari and Firefox, respectively. Now imagine Fluid + Decaf: you can quickly build a desktop application that talks a web services, with Ruby code from end to end! It's huge!
[1] http://fluidapp.com [2] http://en.wikipedia.org/wiki/Mozilla_Prism