Ah, I didn't dig deep enough. There is the bit about $153 million in Subscription Services revenue which they say is due to mainly the monthly recurring revenue. Their Merchant Solutions seems to be related to the payment fees which is $208 million. My guess is a majority of the stores do not sell a significant amount of merchandise (so the monthly fee is a majority of the Shopify merchant cost) and merchants who do sell significant amounts of goods are able to negotiate a special lower payment fee rate (which most merchant platforms do).

From the growth numbers listed in the report, the gross merchant volume (and therefore the Merchant Solutions revenue) is increasing so maybe more merchants are being successful or the existing successful merchants are selling more. The Merchant Solutions revenue is growing about 18% faster than Subscription Services.

Shopify seems to be trying to make more merchants successful (more merchants selling more goods) versus just making it easy to open (and close) unsuccessful stores.

Hopefully Shopify is able to capitalize on increase in merchandise volume if they haven't been able to negotiate a good deal on the payment processing fees themselves. While they might make profits (and not just revenue) from their monthly fees and their App Store, I just can't imagine a merchant platform which does not capitalize on gross merchant volume since that's where the significant profit comes from (like eBay, for better or worse).