It's not that the older ones won't do it, it's that we are always hoping the newer ones do it easier and better.
For example, I could still be playing a Technics KN2000, BUT there was virtually no memory. Everything had to be loaded from floppy, and a single-side one at that.
The newer boards have eliminated external effects processors, vocal processors, harmonizers, tone modules, drum machines, mixers, samplers, sequencers. For example Yamaha made a tremendous advance in the quality of the drums between PSR 9000, 2000 and Tyros.
Now what will the next one add? MP3s? Wavs? CD recorders? Digital Recorders? Which features to we need or want? That's up to you. That's the enticement of the "next greatest thing".
To answer your question--Yes, I could do just fine with what I have for years to come. But I don't want to.
DonM