Scrolling is something that is almost synonymous with the way we use applications these days. The huge use of handheld devices (Apple included) have helped to ensure that.
There was the age old argument of putting things above the fold but in all honesty I do not really believe that this is a sticking point anymore primarily because of the aforementioned and the statistical eveidence out there to support that.
To answer your question, I don't like to base UX decisions around "philosophy". It's based on evidence. So many UX designers go through the throws of research, people interaction and so on to eventually arrive at an educated answer.
Now no one app is the same. All web apps have different audiences, needs, user inteligence levels, user goals and user frustrations. So in Shopify's case, they did it likely for a substantiated reason. If the right hand pane generally scrolls a lot, then this may have been a reason.
Whilst it's fine for people to scroll, why make it any harder to get the user to "do something" may have been their reasoning.
Which brings us to your reference around "call to action buttons".
What you are referring to as call to action and form based buttons has no defrentiation Amir. They are all call to action buttons. The purpose of any button is to get the user to "do something". A link below with a fuller explanation is listed.
Good luck with your further research.
Sources worth reading: