I have no experience in this, but inspecting the code in the webui for the spinup button shows the following onclick event. So at the very least it appears to me that the button is limiting the spinup to the array? The bash in this thread doesn't do that. And again, the webui button staggers the spinups, versus the bash in this thread which does it all at once. It's very noticeable if you have more than a few disks; you could easily reproduce it yourself, I would think, just by pressing the webui button and watching the disk states, and then spinning down the disks and trying the same thing with the script.
function onclick(event) {
toggle_state('Device', 'array*', 'up')
}