So, first of all I want to say that I agree with you. I feel that this is one very weird example of line of sight that was not fully thought through by the designers when addin the letters for clarification,, because thematically speaking it seems pretty clear that these two areas should have LoS to each other.
However, going by the rules as written, and by the 3 steps told by Pamplerousse, the explanation is that the line crosses a wall and, therefore, there is no line of sight.
According to Pamplerousse, and it is also as the rules are written, you check point by point these 3 things to know if the zones have line of sight:
1) separated by a yellow line
2) share a letter
3) a line between the spots doesn't cross a wall.
In the Batman vs guard on the roof case, they cross a wall and there is no letter, so there is no line of sight. In the other image you are showing of zones that have LoS and crosses that wall, they all have a letter to confirm that. So, In my humble opinion, what happened here is that someone should have written a letter in the "batman" zone so it could share a line of sight to that roof over there, but it was not done so, and so by the rules, they don't have LoS to each other.
It's the best explanation I can think of, and it is (again, my opinion) wrong, as it clearly should have LoS.