For web apps, the front end is becoming bigger and bigger, and the back end is getting less important. Our web app at Weld (web/app creation tool) is 90% front-end code, with a very thin back end. I can imagine that a majority of new web apps being built today are dealing with a similar situation.
Having a monolithic approach to a large front-end app becomes unwieldly. There needs to be a way of breaking it up into smaller modules that can act independently. - Tom Söderlund