Statistics about web site visitors is not an exact science - it can depend on what is considered a 'visit', and how different systems analyse and logo data.

For example, if I visit a website and surf around a few pages and then come back 5 minutes later, is that the same visit or a new visit? What about half an hour later? What about if someone else using the same internet connection visits the same site, but with a different computer? It's all pretty fuzzy.

For concrete5, the statistics built into the dashboard is really very simple and has a bit of reputation of not being very informative or accurate. It will give you an indication of whether you get getting traffic and that's about it. If it was any more complicated, it might slow things down. (I appreciate that it's there as an option, but I normally turn it off.)

So it is very likely that you are going to get different figures. For a lot of my clients, I simply add Google Analytics tracking, or have a check at 'webalizer' reports that you'll sometimes find in cPanel and the like. There's alsohttp://piwik.org/, which I haven't tried yet, but looks interesting. They're all going to analyse your data in slightly different ways so you just use the data as a guide to how things are going.