I would assume you could tune or adjust your interests over time, similar to any other user specific preferences.
To your second point it is merely a matter or design choice. Does "funding stories as a whole" trump your more specific interest of Facebook IPO or does your specific interest in Facebook's IPO trump your desire to opt out of the funding stories as a whole.
The problem I see is making such a system intuitive to your user base and clear. It seems the more complex the system is the more complex the user preferences become.
To your second point it is merely a matter or design choice. Does "funding stories as a whole" trump your more specific interest of Facebook IPO or does your specific interest in Facebook's IPO trump your desire to opt out of the funding stories as a whole.
The problem I see is making such a system intuitive to your user base and clear. It seems the more complex the system is the more complex the user preferences become.