1. Web development can be challenging. Writing a simple blog or wiki system in PHP might be "easy", but creating a wordpress.com or wikipedia.org is a whole different ballgame. Latency, scalability, architecture, high availability, manageability, security - the challenges are endless.
2. I don't understand why software developers tend to value the "difficulty" of the technology used in a product over the utility of the final product to end customers. Creating a web app in PHP for sharing daily tidbits in your friends' lives may not be as challenging as writing a compiler for a functional language like Haskell, but its end value may far eclipse that of the latter. Facebook and Twitter after all started as fairly simple applications but are multi-billion dollar companies now. I would even say that there is a certain unix-like elegance in using the easiest, simplest technologies to create the maximum returns in terms of utility to humans. And that, IMO, is far from being a "brain-dead" skill.