Adwords and Analytics differences

[Mong]

I have always witnessed little difference between adwords clicks to my websites and google analytics referral figure.But from last few days it has increased too much like
Adwords -> Site targeted campaign is showing 147
Adwords -> Keywords targeted campaign is showing 182

But urchin is only showing 137 referrals from pagead2.googlesyndication.com

Where is problem and which is more reliable data?

[digiweb]

Google can't count?

[Mong]

So far "yes" there is difference in adwords and urchin figures.