There are a lot of people that are always on the go and that includes Web developers, and so it makes perfect sense that if there was a way they could use their iPad for their development tasks, this would be of real value to them.
The latest news suggests that this is a real possibility. It may not be the perfect solution but, there are some things that may just work.
One of the greatest tools that a web developer relies on is a text editor. The Textastic can be accessed with the iPad and for one that is more powerful, there is the Diet Coda which has SFTP capabilities as well as a SSH terminal.
iOs Vim and Firebug Light
It is possible to run Vim through one of the terminal emulators. Running Vim on the testing host means you can get the files onto your device, then edit them with a text editor, and then transfer them back to the testing host. The only thing you will have to watch for is CPU usage where they may be a risk of timing out, but being careful when using the GNU screen should eliminate that issue. You are going to need debugging tools and you may find that Firebug Light will work perfectly.
To get you started, you are going to need an SSH client app for your iPad then you can get access to VIM, you will need a remote server for viewing files.
At this point, these are educated guesses by experienced web developers so it may be a hit and miss at first and a lot of experimentation. As more people become interested in this, no doubt those that are trying it will share their progress and it will help those who are trying to master it.