There is a built in statistics package (the "Statistics" tab in Edit Mode) that would probably have the data you need.

Here's an old article about it: Did you know that there is a built-in statistics function in Edit mode?

I took a look through the API, but there doesn't seem to be anything to grab the stats in aggregate.  You get the stats for a single page, but I don't see anything to grab them all at once (admittedly, I didn't look very far).

(I thought perhaps you could drop straight to the database, but after 30 minutes of curiosity, I've determined it isn't easy.  Statistics are logged through log4net into -- as near I can tell -- the SqlObjectStore.  I got a little lost at that point, but suffice it to say that it's not just a simple, flat table.)

I'd recommend using an external system like Google Analytics, the built-in statistics is something we are phasing out for something better.

Have a look at this for inspiration on Google Analytics API:

http://labs.episerver.com/en/Blogs/Johano/Dates/2009/6/A-stab-at-the-GoogleAnalytics-API/