Nowadays that's plainly not true anymore because chips hardly get faster year-to-year, but also my 2012 phone lasted 5 years before software support started to get mediocre for Android 4.4 (the hardware was still fast enough and the battery you could still replace in 20 seconds). I've only ever bought new phones for software support reasons (scheduled obsolescence) or because the GPS chip broke after they stopped supporting rooting and so I couldn't get it repaired (out of warranty) without forfeiting that.
What phones do you buy that you feel they're unusably slow after only 3 years?!