Re: v4.2: Mobile Web Interface
The problem with a simple "minus" on the wishlist counting as a "plus" on the inventory is that generally users have very "unspecific" entries in their wishlist like "two Mountain cards". When they add them to their inventory, then want to add "two M10 Mountain cards, one Slightly Played English, one Near Mint Foil French".
That's why you usually need to provide a way for a detailed card input. On the desktop, you can use the in-place-editor to remove one from wishlist, and then click on the inventory count next to it, which opens a detailed card editor.
For the mobile interface, right now you can only click on the card name and then use the controls there to add a new detailed card to your inventory.
In the edition checklist view on desktop we do provide these "Plus" buttons which assign defaults when you add to your inventory, because it was sort of built with that in mind and is more verbose in explaining what happens exactly when you click the "+".