Not sure if it's in "style" or whatever. But, I do believe it's just practicality: Older amps, particularly those no longer being created (and/or the company itself is out of business) are difficult (and potentially pricey) to get repaired. New amps, which tend to be Class D amps, have warranties on them. They're oftentimes easy to get fixed from an authorized repair center, or just by shipping to the originator (the company itself). Side note: Acoustic Image not only has lifetime warranty on their amps, the warranty is transferrable from owner to owner! Thought I'd just mention that. I know of nobody else that does this...could be wrong there. Cheers.