If you publish you WFS-T with ArcGIS for Server you can edit spatial data via the "Built-in" Feature Service which provides much more funktionality than a WFS-T.
But you are right it would be nice to be able to edit data from a WFS-T in ArcGIS for Desktop which is provided by non esri-server.
I agree with the previous postings. Even though using Feature services provide a better solution than what WFS-T provides, being able to edit WFS-T created with ArcGIS and with other Server platforms is something that have been lacking in ArcGIS for a long time. I would love to see this implemented if at all possible.
It makes no sense that ArcGIS Server can offer WFS-T services, but ArcGIS Desktop client can only view the data. You should be able to insert, update, delete...
Especially since open source software can do this as well. This is a great, perhaps essential feature missing in ArcGIS.