As far as I can tell that's actually what they did say:

"We are delighted to announce that the six General Partners of Andreessen Horowitz, with our families, are all committing to donate at least half of all income from our venture capital careers to philanthropic causes during our lifetimes."

http://bhorowitz.com/2012/04/25/our-philanthropic-commitment...

I think it's an extremely positive statement for them to make.