In reply to:
perhaps he did intend it to be a criticism of Madonna, and decided that he didn't want it to get too much attention
That would be a shame. I delight in hearing a good songwriter attack another artist through their own lyrics. One of the most prominent examples is Lennon's How Do You Sleep? but Bowie has some even earlier examples, for instance Song For Bob Dylan.
Song For Woody - Hey Hey Woody Guthrie. I wrote you a song.
Song For Bob Dylan - Here this Robert Zimmerman. I wrote a song for you
Material Girl - We are living in a material world. And I am a material girl
Lucy Can't Dance - But you can't buy me off in this serial world. Who died and made you material girl?
The Last of the Dreamers