Originally Posted by: dlwalkeI get that different classes of pickups (e.g., humbuckers vs single coil) and configurations (e.g., series vs parallel or neck vs bridge) make a big difference in the sound.[/quote]

They can. But the difference is often difficult to isolate considering all the elements that comprise any given electric guitar tone.

Originally Posted by: dlwalkeBut when I listen to videos that compare different pickups of the same class (like a stock strat p.u. vs a particular Seymour Duncan single coil replacement) I most often am hard pressed to hear any difference.

It definitely helps when those demos use a scientific approach: use the exact same guitar, amp & settings, player, playing the same music, using the same recording process.

But many product demos are obviously going to adjust the process to put the product in the best possible light. That's natural of course. :)

[quote=dlwalke]To the extent that they are different, I am wondering if it is just about output and frequency characteristics. If that's the case, it seems as if these are things you could just as easily accomplish using the guitars volume and the guitar&s tone/EQ controls. Or am I wrong about this?

Sometimes that's possible. But consider that most specialized gear is optimized for some specific purpose. This particular pickup is a great blues pickup for Strats. That one is a great high-output pickup for metal. This other one is great for classic rock rhythm playing. And so on.

Having a pickup that is designed & built for some particular purpose is going to be much more beneficial in achieving some particular tone. As opposed to having one that is average, then trying dial in your amp & effects to compensate for the rest of the signal chain.

It's like having a specific rachet size is better is certain situations than trying to use an adjustable wrench. Make sense?

Another important aspect about different pickups is how they respond to your playing. How it feels to play through them yourself. And this can be described in demos. But there's simply no substitute for actually playing through a set of pickups yourself. The way any given pickup responds to your individual pick attack, articulation & overall playing is a huge factor in whether or not any given pickup will work for you. And sometimes that even means adjusting your playing to get the right result from the pickups (or any gear for that matter).

Hope that helps!