After watching the new video from Google below you will see why. I also got from the video that the examples given are rock solid proof of how much Google relies on links and anchor text http://www.youtube.com/watch?v=KBdEwpRQRD0 What are your thoughts?
I'd guess that what sarirejo is doing is the only solution for keeping them from indexing any part of your site..
If you have your urls already in Google's index ... using a robots.txt to block them will not remove them from the index, but you're simply instructing Google not to crawl them again. That's why you don't see the cache any more! To remove a url from the index, there are other methods.
The only way to get the url's removed is to add a noindex tag to the page that you want removed, and make sure that the page is still live on your server. But even when you do this it can still take forever for google remove those pages, I have pages still showing in the index even though they have a noindex tag, in other words google will remove them when they feel like it.
Just to clarify, that's a meta noindex tag as discussed in the video, not a noindex tag in the link. It was stated in the video that even with the disallow in the robots.txt file, the page may still be listed in Google. The only way to remove it completely from the index was either through Google Webmaster Tools or via a meta noindex tag on that page.