Why I think Stern isn't included.
I think Sirius excluded Stern because the company would lose customers that are paying for "best of both". I'm sure they have all the statistical analysis, and I'd bet that most that pay for "best of both" are XM customers that want to hear Stern. They pay $16.99 instead of $12.99.
If the company put everything from both XM and Sirius on the internet, they could have customers switch from a $16.99 package to a $12.99 package. Some would pay the extra $2.99 as well, but you're still taking a hit to revenue that I'm sure the company is absolutely paranoid about doing. They are (I hope) watching every single nickle at the company right now. They are probably realizing now that they're being "penny wise, pound foolish".
They just be waiting for new revenues from iphone streaming to equal the potential loss from customers dropping "best of both".