I think its normal if you don't do anything to build quality links.. google calculate your backlinks, they give more weight to relevant and quality links that you have in your site. So if you want to have a high pr, go and build quality backlinks..
Use Google Webmaster Tool to see your current amount of backlinks and try to build more back links. So that, your PR green value can move on high value..
If you continue building links for the past 3years and your PR didn't changed at all... That's a big problem... Focus on getting relevant and quality links for your site to gain better PR... Oh well, the green bar isn't that important anyway...
Just stick around popular blogs and they will appreciate you with quality link.
__________________
My name is Sergey Rusak and my websites and blog is here....
Have marketing or SEO question? Submit form on one of my sites.
Follow me on Twitter!
Go to seomoz, and find out the acual power of your website it may be the same or it may be better. One of My sites went from pr4 to pr3 after the update dropped to pr0 and went back up to pr2 all in the same update. the only thing that hasnt changed in this web site is SERP its been #1 in various amount of key terms for 3yrs. running with out loosing its positions.
my sites pr2 right now
seomoz says the (strength)pr4