I think it depends quite a lot on where you draw a boundary between applications (i.e. what is your definition of an application), and what use-cases you take into consideration.
While you could implement a web browser as an amalgamation of
As for piping the data to an external process - that is how it actually started. If you are concerned about the size of an average web-application code, yes they are often big (and often because they are a layer sitting above a platform written in an interpreted programming language rather than a "simple" application), but compare it to their equivalents. Email clients, office suites........ you name it. All of these are quite complex and have too much functionality to be implemented as a couple of processes communicating through pipes. For the tasks you are using these applications for are often complex too. There are no good simple solutions to complex problems.
Maybe it's time to look a little beyond motivation behind the UNIX motto "applications that do a little but are good at it". Replace "applications" with "general modular units" and you arrive at one of the basic good programming practices: do things modularly, so that parts can be reused and developed separately. That's what really matters, IMHO (and the choice of programming language has very little to do with it).
p.s. (following the comment): In the strictest sense you are mostly right - web applications are not following the UNIX philosophy (of being split into several smaller standalone programs). Yet the whole concept of what an application is seems rather murky -
sed could probably be considered to be an application in some situations, while it usually acts just as a filter.
Hence it depends on how literally you want to take it. If you use the usual definition of a process - something running as a single kernel process, then for example a PHP web application interpreted in httpd by a module is the exact opposite. Do loaded shared libraries still fall into the scope of a single process (because they use the same address space) or are they already something more separated (immutable from the point of the programmer, completely reusable and communicating through a well-defined API)?
As for the textual interface: note that what was true for data processed 40 years ago is not necessarily true today - binary formats are cheaper both in space and power required for de/serialization, and the amount of data is immensely larger.
Another important question also is, what has actually been the target of the UNIX philosophy? I don't think numerical simulations, banking systems or publicly accessible photo galleries/social networks have ever been. Maintenance of systems running these services however definitely has been and likely will be in even the future.