To me, it's the loss of control that appears odd. Direct sales to customers is, as you say, smaller revenue stream than their customer dealers.
Buying into the Shopify model means doing things the Shopify way, that's the Web framework you must use. Now if Shopify provides everything Gibson wants to do, that's fine, but if Gibson wants to do things that Shopify can't offer, then they have to either build something off the Shopify site and link back and make sure it all fits.
I can't speak for USA accountancy rules, but in the UK you could get this as a managed service through a Web design and hosting company and get the people costs off your head count. You also get the VAT back and it goes against corporation tax as an expense and HMRC are happy.
For smaller companies Shopify simplifies things but for larger ones, I still think it's unusual.
Clearly Gibson will have worked it all out and made their call so what do I know 😊
Rob