Strange Search Engine behaviour

It has been a while since I noticed same strange behavior from Search Engines, in mean of traffic driven to my site.

First thing I have noticed - in days, when I get referral traffic, search is down. It then comes back normal in days when there is little or no referral traffic. Strange right? In this case I'm speaking about Google.

Then there is another pattern, what makes me wonder - I gotta feeling that Google is somehow limiting how many Search results it's driving to my site per day. Once reached some level, it stops sending me visitors.

So let's say, if in week I receive about 125 visitors from Google, Google will divide that number by day count in week and send me average 17.8 visitors per day. One day Google will send 30, second 20, other 25, then 18. And if Google will send lets say 20 visitors 6 days in row, in 7th day, it may send me 5 visitors. So making it again 125 visitors per week.

Take a look at this screenshot, from my Google Analytics account:

As you can see there is constant Organic search traffic for 3 weeks, and it seems it will stay constant for this week again, making it constant for 4 weeks.

Now look at this screen, where organic search traffic is showed by days:

Now there it seems, I'm having actually more visitors as time goes, but as you can see there is days, when Google stops sending traffic, and makes it even if compared as week view.

Strange, right?

I really don't know - what does it mean? I'm hoping that in month view I'll experience traffic increase.

If you know answer - Why Google is treating my sites, this way, please leave me a comment.