There is something about the ability to translate what you've been working on on any surface and in any setting to any other surface and any other setting. I don't really know what it is. But you know those guys who can just sit down at any kit, not adjust the height or angle of anything, bass drum pedal is set up in the exact opposite way they like...yet it does't seem to affect them at all? That's definitely not me. I think a lot of that is experience sitting down at random kits and making it work, but I think the main thing is just big ears. What are big ears to me? The ability to accurately hear what it is you're actually playing (not what you imagine you'd like to be playing) and quickly make the adjustments to make it sound like you want. I don't know how to develop that, although I think anything can be developed if you can find a way to break it down. For me, pad work is great for ingraining motor patterns and learning parts. I have to practice it on real drums to make it musical. But I think there are those guys who can work it out on the pad, and go straight to the kit.