Should the penetration of the latest version become a problem, it can be dramatically improved with (semi) automatic updates of desktop clients and availability of (semi) official binaries for various *nix flavors.
Current desktop user's are either not aware they can/should update, or they are not certain the upgrade will not mess with their wallet and they don't bother to spend time to verify that. The majority of desktop users are to lazy to upgrade, unless there is serious functionality upgrade, they are aware of.
The majority of server administrators like to yum / apt-get update daily/weekly/monthly, but when it comes to compiling the code, it takes effort to read through release/upgrade notes, backup wallet, etc, so they don't do it as frequently.
Automatic updates seem unlikely as a bad idea and has been discussed. I think anything involved with Bitcoin core is covered. But if Debian/Ubuntu/red hat package managers do their package updates quickly, that helps. :-)
Quote from: gmaxwell on September 13, 2013, 08:39:10 PM
If the core developers start telling you that you need developer controlled automatic update you can assume that we've somehow been compromised.
https://bitcointalk.org/index.php?topic=293824.0