Why not non-profit, like Wikipedia? Especially if they ask for donations. I can understand somewhat the Ripple folks, but Bitcoin?
It's a 501(c)(6)— a professional league, not a 501(c)(3) charity.
A 501(c)(3) engages in religious, scientific, educational charitable purposes and are obligated to act in the public interest. They're prohibited from certain political activities (they can lobby for their interests but cannot support candidates and lobbying must be limited to some minority part of their expenditure) and must meet various tests for their funding coming from the public (or other charities and government) sources. The IRS has been clamping down on charity applications now and seems to be demanding more justification that an organization's purpose is in fact charitable. The plus side of all this trouble is that donations are tax deductible, and there is a certain degree of public legitimacy created due to both the charitable mission as well as the public support requirements demonstrating that the org isn't just acting in one parties interest.
501(c)(6) organizations are professional interest organizations such as chambers of commerce, sports leagues, etc. Rather than acting in the public interest they act in the business interest of their members. (And their income is not taxed, because it's assumed to already be taxed— and only replacing activity that the members could have done directly, but it is not tax deductible).
The lobbying and political limitations as well as the general hoop-jumping to get the classification are reasons that if I were creating a Bitcoin Foundation I might consider making it a (c)(6) instead of a (c)(3). On the other hand, the lack of a requirement to serve the public interests will likely always feed accusations of the organization being a pawn for its primary funders, and along with the lack of deductability are arguments against (6) and in favor of (3) most obvious to me. IIRC there are also fewer rules about the disposition of assets which can make it easier for a large sponsor fund a (c)(6), because IIRC a (c)(6) can return assets to people where a (c)(3) can only dispose of assets by transferring them to another charity.
I think that even if we had a 501(c)(3) Bitcoin org, the Bitcoin ecosystem would still probably need a 501(c)(6) one to optimally enable collaboration of the large commercial interests.