I'm not a keys player but I have a feeling if rashbaum sees the thread he'll back up the fact that keyboards in general are MASSIVELY more powerful than they were back in the 80s so that's not a reason for the sound being "thinner". In fact, with patches being made up of more and more layers now, you can get immense amounts of depth with the polyphony on modern keyboards when compared to even keyboards of the late 90s.

The recording device used to capture a performance, personal taste of the musos and sound engineers in control of the mixing desk, the venue's acoustic properties, the changing instrument models/brands etc., will all play a role in dictating how the tone comes across.

With respect to the guitar tone, You have to remember that Jon also plays teles live which have a naturally 'thinner' sound than say a Les Paul or even a Strat anyway.