Make sure to check out George Carlin's piece on motivation per se - that makes everything clear, I think ;)
The term is a bit overloaded, don't you think? It might have had some meaning ten years or so ago, but know there are so many practitioners (if you can call them that) so as to dilute the term to silliness.
First, I've always thought that bringing in a motivational speaker is a admission of failure on the part of a company. "We aren't intrinsically motivating ourselves, so here is a cheerleader for you". Provide meaning, mastery, and autonomy and you'll never need external motivation for your organization.
Second, the speeches themselves are mostly filled with non-actionable fluff.
Motivational speaker stresses the wrong thing for me: Whoever speaks about plans, the future, new ideas or something similar should do it "motivationally". But the focus should stay on the content or better the transportation of the message. The motivational part comes as "how things are transported". Motivation for motivation only is like asking someone to run faster instead of telling him where to run. In short: I do not like the term.
As far as I'm concerned, the term "motivational speaker" has too much baggage associated with it.
Bear in mind that my exposure was during my life as an employee, where "The Organisation" would use "motivational speaking", as part of their annual kickoff, to attempt to cover up the fact that the people who developed last years plan (that failed misreably because it set unacheivable or unrealistic goals) are the same people developing this years plan that (that will failed misreably because it sets unacheivable or unrealistic goals).