Really? You can build non-web apps just as fast as web apps. There are decades of tools and programmer experience doing this daily. You can't build Autocad or Photoshop as quick as you can churn out a buggy Rails site, but that's comparing apples to oranges.
Most of the arguments in this thread are coming from two totally different perspectives. Some holding doggedly to various ideals and dogmas and instead of trying to learn the new domain, they try and make the apples look like oranges. This never works. Most are right about this or that when it comes to the domain that they are experienced in, but when economics forces people into a new problem space some don't try and learn the new space as a thing in and of itself, instead they try and adapt their methodologies and abstract to a different problem space they are more familiar with. That is where these conflicts come from.
I expect the underlying point was that most popular native platforms today almost force you into best practices which does add some upfront cost.
On the web you can throw up a single page PHP script full of SQL injection vulnerabilities and Javascript spaghetti and you are off the races. There is generally no equivalent for a modern GUI system. You typically need to start with a full MVC infrastructure in order to even begin to interface with the system libraries.
When you take care to craft your website using the same best practices the differences become negligible, but a large number of developers do not care about architecture and can take shortcuts that make it feel like they are moving faster.