Windows internally implicitly supports / as an alias of \.
Note that Arc provides its own http-server which is not very directory-based (rather, something like http://example.com/login would be defined with a (defop login ....) form in the running Arc process), so I'm not sure why you're routing to a directory.
The deal with path separators has to do with the difference between the classic Mac OS (9 and lower) and Mac OS X. Classic Macs used their own path system, which used :s as the path separator (e.g., ":Macintosh HD:Documents:Arc:tut.txt"). When the switch to OS X came, suddenly everything was based on Unix, so file paths became sane (e.g., "/Users/username/Documents/Arc/tut.txt" or even "~/Documents/Arc/tut.txt"). Nevertheless, in the name of backwards compatibility, many things still display paths in the old format, the GUI pretends that :s in file names are actually /s, and AppleScript deals natively with old-style filenames.
