Yes, they are. By definition it is a fallacy. Slippery slope arguments, by definition, are missing the connecting tissue.
Well I guess it is now that you've changed the Wikipedia entry for it and changed "argument" to "fallacy."
The slippery slope argument only becomes a fallacy if you make an unreasonable conclusion connecting happening A and happening B. Folks were debating the merits of including ~3,000 victims of 9/11 individually as articles in Wikipedia. Asking what this means for other victims of other disasters and crimes around the world and in history is not a far stretch. That is why "rounding up" all arguments of this type to fallacy is not fair.
You seem to have a basic misunderstanding of logical fallacies.
"The slippery slope argument is usually used as a commentary on social change, not as a point of logic."
(which used to be in the Slippery Slope article)
-Fuzheado