Absolutely agreed... prototype-morph-prod is a faster cycle.. but on the same lines, it means automated unit tests are more important the more complex projects get. Which is why modular code and testing work really well with scripting environments, and computing is fast enough.

With a modular approach, it also becomes easier to scale horizontally either in the same server/system or a separate server/system. Either via HTTP, TCP, 0mq or another abstraction, if the interfaces are the same, the modular layers can be replaced. This gets easier with async by default environments (node.js, golang, etc), and I find it to be much harder with classic N-Tier (.Net, Java). I'd rather use 0mq with node than wcf with .Net any day of the week.