I imagine this has been asked but there is so much focus on backlinks but in reality while people pay so much attention to it, the fact is link:sitename.com shows a very small fraction of the links. For example, I have some sites that for example on Yahoo show 50,000+ backlinks and many of them are PR5 to PR7 and yet when I do a link: Google shows less than a hand full. I guess ultimately, why?
If you log into your Google Webmaster account you'll get a much more accurate representation of links.
I do remember that they released that very recently. I only wonder why it's not so clear on the front end.
I'm pretty sure they do it so that your competitors can't go after your links. Yes, Google Webmaster tools will reveal more. Sometimes it takes a LONG time to update though. Yahoo has a good list of backlinks without having to login if you like.
I'm not disputing that. They may show quality backlinks in the Webmaster tools, but on google.com if you do a search for links to your site, you won't even see all of those.