On the contrary, it is a very well thought out decision. If you’ve looked at the instance we’ve set up, we want to support various langauges given our global user base, and top level categories are therefore being used for that bit of organisation. On discussion.fp.o, since it is community development oriented discussion, the language we generally limt ourselves to is English. So, creating categories to manage languages and all the dev talk and user-end discussion is very hard in one instance.
We should also keep in mind that using discourse by e-mail is a feature, but that is not the primary mode via which discourse is meant to be used.