Oh, that might be true, I do remember encountering some escaping issues when creating a more complex POSIX (or bash) script that involved lists and iterating through stuff.

I see Bash only uses commas in Brace expansions:

file{1,2,3}.txt # file1.txt file2.txt file3.txt

I guess it would only be a problem if you want to expand

    file,.txt   
    file,,.txt   
    file,,,.txt

Imagine seeing this code:

    echo file{",",",,",",,,"}.txt