I expect it's possible to get a shorter program that is still pretty legible, but that you'd have to use a little language that's almost purely declarative to do so. Arc (like other Lisp dialects) is not only brief but flexible.

For example, this is short and clear (to me, anyway):

one: form two, text foo
two: link three, "click here"
three: say "you said: " . foo
[download]

This example, though, is of a language that describes only web page interactions or screen-based applications. It's not a general language with a few functions or macros related to the web along with the ability to handle any other type of program. Its syntax is dedicated to the one type of task. It's also not a popular (or even implemented) language.

Arc itself may not be exactly mainstream yet, but as a Lisp dialect it's familiar enough to a wide enough audience. It's certainly reasonable to expect that the challenge specifies popular languages, and could have also specified that the languages be general-purpose.