Where do I get current general statistics on how many users get past homepages?

Did you look here?

The most compelling argument you can make is based on the statistics from your own site. Do you track your visitors?

I would agree with @cwilbur using such a generalized stat is going to be useless for your own site. I had a similar request made from a senior manager who wanted to know what the average of our industry was for something. While a bit more relevant it just does not take into account the differences that may be required by the business and unless they are prepared to change those things then that number is unrealistic. Get the stats from your own site and decide if there are things you can change to improve the “bounce” rate.

Give Google Analytics a try. It’s very easy for beginners.

http://www.google.com/analytics/