I am fine with the way Asana works. This puts one in the need to re-read the comment before posting, that is “Good Thing ™”. Such re-reading not only makes one correct spelling errors, but also allows deeper restructuring comment to make it better.
The Asana’s approach still allows for corrections in fast interactive workflows, when task comments are considered to be chat-like, i.e. when one had written one-liner comment there is no need to re-read before posting, you just post it, then read it, and you stil, have 15 sec to re-edit it, in case you noticed spelling error or something. Other participants of this interactive workflow will be treated properly as well, they’ll see your comment for a short period of time and then it’ll disappear while you correct it, and will get it again once you post it.
There is a lot of mental mechanics built into Asana comment editing rules, and I think it is quite good to highlight Asana product amongst competitors.