In the real world, distinctions are made between shareholders, directors, investors, partners, actual management staff (such as CEOs), etc and the legal responsibilities of those people are different.  A great deal depends on what people actually do in respect of a company's operations rather than the title they hold - many protections from liability only apply given certain circumstances (for example, not being an "official" director generally won't protect you from liability if you've been undertaking the activities a director undertakes, investors are often only protected if their role is restricted to "safe harbour" activities).

A lot of Bitcoin enterprises represent themselves as "companies" and use the language associated with companies when in fact they are sole traders (which appear to be the case with usagi) or general partnerships (which appears to be the case with BitcoinGlobal and GLBSE) - entities which are totally different in terms of liability.