My one year old Nexus 4 is on KitKat. I guess you're talking about the Galaxy Nexus. While I agree with you that they dropped the support a way too soon, being the reference phone you'll have no problems in updating it with CyanogenMod, which is a really good distribution btw.

But as a slight counterpoint, given the fast release cycle, you can't expect them to support a phone forever. You mentioned iPhones. Well I have an iPhone 3GS. It's a perfectly capable phone that still works and that was still sold as the low-price alternative after iPhone 4 happened, yet Apple stopped supporting it as well. But I can understand that, because these OSes get more bloated with stuff and it leads to a shitty experience. I was able to upgrade an older Galaxy S (first generation, shipped originally with 2.1) to 4.3 by means of CyanogenMod and it was unusable due to the less than capable hardware.

Google did drop the support too early for the Galaxy Nexus, but try out CyanogenMod. I'm even thinking of installing it on my Nexus 4 because the Android on this device is bloated with Google-stuff that I cannot uninstall and it pisses me off. It's also enlightening to install CyanogenMod without Google Play, for an all open-source experience ;-)

There's test builds of Android L for the Nexus 4 available, so it looks like it will also officially get that release. It's still got 2GB of RAM and a quad-core 32-bit ARM, so it's not too different from the Nexus 5 in that sense. It is really a question of how long Qualcomm will support the S4 Pro board support package. If we've all moved to 64-bit ARM cores, then that'll be a bigger problem for these older 32-bit phones.