Many hanzi have a roof on top, including a dot. From the HSK2 list, we have:
客 家 字 完 室 安 它
The commonly used hanzi 写 is unlike these because it does not have a dot on top.
I'm wondering if there's a reason the hanzi 写, in particular, does not have a dot.
Question: Why does 写 not have a dot on top?
(Another exception I can think of is 买, which has the radical 乛 on top, but it has a counterpart 实 with a roof.)