* With an Android device, the manufacturer outright abandons updating the phone the moment their next handset is on sale. (Samsung seems to be the worst about this, but, even Google has done it to stock Nexus phones.)
This is wrong. Samsung supports its S series devices (S2, S3, S4, etc) for a looooooong time. S2 got updates till KitKat. And with every update it got faster, not slower. They even back ported some of the features they introduced on later devices (Smart Stay, etc).
Nexus devices have guaranteed updates (on the same day of announcement, too) for 18 months. The new Android One handsets also have guaranteed updates. It should be noted that these updates are from Google so they are very quick and very frequent, sometimes to the brink of annoyance.