I've never heard about any web application that can just "scale" without some growing pains. Sure it's possible to pay for some elastic IAAS or PAAS, but that really does not solve any scaling problems. You still use as much resources per user. To increase the effectivity of the application, one has to either grow it over time or built right from the start. To get it right from the start can be a huge sub-optimization if you miss something and must do it over anyways. That is why most start "quick and dirty".