The apps are also evolving. Compare Facebook today to what it was two or three years ago. The app does a ton more and all that extra functionality doesn't come for free. I suspect one of the primary reasons they broke messenger out into a separate app is that the Facebook app was simply too damn big.
There have been instances where an upgrade has made my experience better, but the trend has definitely been in the other direction (for me anyway).
I also have another concrete example: the original Nexus 7 had an SSD that didn't support trim. Over time it became nearly unusable as the SSD became fragmented. It was also severely bandwidth constrained. The device was decent until the first major Android revision came out. At that point, the new version of Android so significantly increased the bandwidth requirements on the SSD that it effectively strangled the device.
What was an awesome device the day I got it became absolutely unusable. Eventually I installed a version of CyanogenMod and formatted it with an SSD friendly file system which made it passable again but, still sucked compared to the day I bought it.