For posterity, there’s a few different things going on here.
First, the reporting engine we use automatically inserts the dividers, and it’s not really feasible to style them individually (for instance, dividers are shared between adjacent cells, so which cell’s formatting settings would ‘win’?)
Second, there are some properties that control (per-cell) whether it will render its dividers…but they weren’t explicitly exposed to the end user.
Right now, what you can do to manipulate the dividers in a simple table or crosstab is change the ‘Style’ at the top level:
It defaults to ‘None’ (which is wrong), but if you change it to some other value, then back to None, your table will not have any visible dividers anymore (you can try using the other styles to control your dividers as well).
In 8.1.12, each cell will have its individual top/left/bottom/right divider properties exposed, so they can be manually changed in the property inspector.
You’ll still need to jump through some hoops (such as disable the right divider on cell A, and the left divider on cell B) to hide the dividers, but you’ll at least have full flexibility.
In terms of more exotic styling, you can (as you always could) configure each cell with its own border, fill, and other styling; it’s just now a lot easier to remove the automatic dividers you don’t care about anymore.