Earlier quoted context omitted.
Yes, Open Sans is under the Apache License while Public Sans should be under Public Domain (although this is a bit unclear and is being debated in the github issues).
While that's a great reason in the US, internationally unless it's under the CC0 or similar the Apache License is actually preferable to Public Domain (assigning things to public domain is not trivial or even possible everywhere)
Note that this doesn't apply to non-USG-made derivative works, though.