The latter usually arise from pre-existing relationships between one or more of the founders and the advisors. Normally, the advisor is someone who wants to assist the founders and whom the founders accordingly want to reward by small equity grants via the advisory director role. These types of advisory boards, in my experience, tend to be of significant value to early-stage startups and are well worth the small equity grants involved (which, by the way, tend on average to be more like .1%/yr of service rather than the higher number suggested by the author of this piece). The informal nature of the relationship also avoids many of the hassles associated with trying to have such an advisory board meet from time to time in some formal manner. In essence, what you have with such boards is a healthy working relationship from which all parties benefit.
The "window dressing" variety of advisory board is often as phony as an undersized glass eye that spins randomly with every blink. This often involves the so-called industry luminaries used to make the startup look much more impressive than it really is. In essence, such advisors hire out their names (and, yes, they will insist upon larger equity grants and often for some form of cash compensation as well, as for example for every meeting attended). While one can never say categorically that such advisors do not add value to a startup, their primary function is to add name-value and hence the value of their contributions apart from name value tends to be limited. There are exceptions but, in my experience, not many. In general, these types of advisors are a clear mis-match for most early-stage startups, though they often help later-stage ones needing "company profile" dressing for IPO, etc.
By the way, founders still occasionally confuse the role of advisory director with that of a board director. There is no connection whatever between the two roles. The former is basically an outside consultant only and has no management-level authority; the latter, of course, has tremendous management authority (and corresponding liability risks as well, which the advisory director does not).
Understand that it feels good to have an 'advisory board' but at the end of the day, the only person who's going to get your biz off the ground is you.
[EDIT: My own experience: most people are more than happy to give advice without being formal advisers]
I like the idea of getting help from people. When/if your startup is going somewhere, pay back for their help/advice in form of equity--as opposed to getting an A-star list put together on day 1 which often just ends up looking shiny but rarely useful.
When all is said and done, you will have to perform and deliver. Embrace whatever you can to help that. If something is cosmetic and doesn't help you, people will eventually see it for what it is.