I have to respectfully disagree. If your 2 year old phone is still running great and does everything you you need it to do that's great, but better hardware, more memory and higher quality screens will always play a major role in the smartphone world. It's not a "marketing ploy", its simply the normal progression of technology.
I didn't "need" to upgrade my S3 to an S5, but the improvement was absolutely noticeable in every area. The same could be said with my recent laptop and tv purchase.
S5 tap'n