Google on its Official Google Webmaster Central Blog informed about changes in their webmaster guidelines. Change was initiated through change in one of their algorithms. In the blog Vanessa Fox said:
“Don't use "&id=" as a parameter in your URLs, as we don't include these pages in our index.
However, we've recently removed that technical guideline, and now index URLs that contain that parameter. So if your site uses a dynamic structure that generates it, don't worry about rewriting it — we'll accept it just fine as is. Keep in mind, however, that dynamic URLs with a large number of parameters may be problematic for search engine crawlers in general, so rewriting dynamic URLs into user-friendly versions is always a good practice when that option is available to you. If you can, keeping the number of URL parameters to one or two may make it more likely that search engines will crawl your dynamic urls.”
Google has given Design and Content guidelines, Technical guidelines and Quality guidelines. According to Google abiding by these guidelines will help them find index and rank your site. But Google has also warned not to ignore Quality guidelines since they discuss some illicit practices which can result in removal of pages from Google index.