I dont understand why you have so much trouble understanding this, not only is it logical that the exponential growth pattern slows over time (and not to mention, its INEVITABLE as the price will clearly not continue booming once adoption and usage is saturated (indeed then there will be massive competition) -- again not only is it logical, it is how the bitcoin growth pattern has functioned- we will probably never see the massive 100 fold or more increases a year again (but thats what was going on at the beginning),
I do understand it quite well and I am waiting for any signs of said slowdown, that's why this whole trend observe thread, what I am trying to tell you is that I don't see any signs, yet. On the log graph, bottom line - since 2011 - is raising pretty much in a straight line. I don't consider 2009 and 2010 because that is statistically insignificant noise, too low volume and too unprovable data. Your graph is fine but useless - you can fit anything with least squares, does not mean it is confirmed by any price swings.
What we might have seen in 2013, was a straight up leg on an S-curve; but to know for sure one more year of 4x growth should have to pass. If that is so, then slowdown might start in 2016-2017.