I have been reading a lot of stuff about HTML 5 recently. Something still looks very fuzzy to me and I hope somebody can help me understand it better.

Is HTML 5 for the "technology" to create the UI only? If I need to create an application to access bank accounts, how is it possible that HTML 5 will replace all other technologies? I mean there must be some kind of web service that the application has to use to access the data on the server and I can't see how that piece can be done with HTML 5.