In light of the topic, I am not giving anyone legal advice nor do my comments intend to replace, compliment, or supplement the enlightened advice of an attorney in your state. In fact, I might be completely wrong so do not rely on anything I say. These are merely my uneducated opinions on the topic at hand.
Interstingly, Legalzoom is a corporation and as such, is not legally allowed to provide legal advice. Many states, allow for Limited Liability Partnerships which as similar to corps. but do not entirely insulate an individual from a lawsuit. In an LLP, one partner is not liable for the malpractice of another partner, but each is liable for his/her own malpractice. Thus, LLPs do not provide absolute insulation from professional liability but the firm as a whole is insulated for another's liability.
Corporations have much broader insulation for shareholders to encourage investment. LLP's aren't allowed to have non-professional investors. Thus, if the LLP is a law firm then only lawyers may invest in the LLP. If the LLP is a medical practice, then only doctors. Basically, most states don't want to guarantee no liability for people in these fields but still want to encourage efficient partnerships. Thus, the LLP was formed.
The fact the Legalzoom exists as a corporation tends to promote the idea that these form providers are not handing out legal advice, at least not under the definition of the states where they provide there forms. Of course, they may be "risking" it and might be in violation of some state's law, but I didn't take the time to go check any individual state's law on the unauthorized practice of law with reference to "legal" forms. There is likely some case law out there with respect to tax forms and wills/trusts forms since people have been publishing self-help books with template forms in those areas for decades.