English is an evolving language and one that isn't controlled by any central authority. English is defined by common use.
Common use with data these day is to use it like it is singular, a collective singular noun.
The one place where there is a holdout on this is in academia, where in their ivory towers they still hang onto the old way of treating data as plural.
I do quite a lot of proofreading for technical documents and scientific documents. If its a technical document, then it is always "data is", but if its scientific it is always "data are".
Naturally this drives me crazy.
As for the oxford comma, i'm very firmly in the camp of using it.