You usually download a browser just once, so turning if off isn't the issue. I suspect some of less technically inclined might abide by it and not download the new broswer.
It almost seems like trial run for stopping the download. I can imagine "clippy" popping up an saying "I see your trying to download a browser, I'm sorry, I can't allow that"
Gmail still nags me about not using Chrome.
I don't see the issue here.