site: vs. inurl:

What's the difference, and why?

[Tellico4x4]

I've had Google traffic tank over the past two weeks on one of our sites, and trying to figure out why.

If I run the site:www.mysite.com in Goggle search, it comes up with 75,000 pages. If I run the inurl:mysite.com , it only comes up with 150 pages. Need some help to understand the difference here.....Also, BTW - before the drop in traffic a couple of weeks ago, the inurl: returned about the same amount of pages as the site: search.