- HBO drives a lot of cable purchase
- Some of that money goes to the cable companies for data carriage
- The cable companies know HBO sells cable
- Any alternative distribution means risks the cable companies losing income
- Cable companies losing income means that HBO risks either being dropped from the cable companies or having to offer them a bigger slice of the pie (since distribution is now non-exclusive)
It is a huge risk for HBO to jeopardize their cable subscriber income with a direct-to-market model.
That being said, I won't pay $100+/month to watch just HBO so do the math on that.
What really annoys me is that this goes so far as affecting, say, iTunes releases. HBO only releases shows on iTunes (if they release it at all) just prior to the next season starting to drum up more interest. That's a trap and I'm not falling for it.
This all goes back to why a la carte cable will never happen (given the current power structure and regulatory environment). It either means people will spend less on cable or things will be more expensive so it won't be worth it. Either way the cable companies lose. Content creators also lose because no one wants to take the risk of losing what is otherwise guaranteed income (a slice of every cable bill).
Years ago, Hollywood went through a shakeup splitting content creation from distribution [1]. It's really time for the same thing to happen with all content industries. We need to separate:
1. Content creation: studios like HBO;
2. Distribution: cable companies like Time Warner and Comcast; and
3. Infrastructure: the actual last mile, cable or fibre infrastructure.
Of course the political likelihood of that happening is essentially zero.
[1]: http://en.wikipedia.org/wiki/United_States_v._Paramount_Pict....
EDIT: to clarify this point, I don't believe cable companies would pursue the nuclear option of dropping HBO. However what the cable companies have now is essentially an exclusive arrangement with HBO. With implied or otherwise, HBO earns a premium for this in terms of how big a cut the companies get. Providing a means to bypass the cable companies would sooner or later result in a higher cut being paid to them, less marketing of HBO by the cable companies to its customers, etc.
Basically there is an economic cost to breaking exclusivity whether it is explicit or not.