New iOS 6 Safari comes with Web Inspector feature which allows to connect to it from your desktop Safari via USB cable. It then allows you to debug pages opened in iOS Safar
Stumbled upon this blog which shows how to debug iOS web app on Windows using a stndalone app by Telerik called AppBuilder. You're supposed to create an account on their platform before using it and it has a 30 day trial.
I've used this on windows 7 64 bit for both vanilla web apps and Phonegap apps both on iPad with iOS 7.1, and it works. You get web development tools very similar to those in Chrome.