Tunisia has a relatively large middle class because of something so obvious it goes unremarked upon: it is a real state, with historical and geographical legitimacy, where political arguments are about budgets and food subsidies, not the extremist ideologies that have plagued its neighbors, Algeria and Libya.
Kaplan provides some interesting history and reasons for calling Tunisia a unique case.
And I'll grant him the case of Tunisia's advantages. But this is hardly the same as saying only Tunisia can have such a revolt. I certainly haven't been calling Tunisia the first domino to fall in the Arab world wave that will follow. Tyrants have much power, and in Tunisia that power was not used because the army would not follow orders to shoot protesters.
It may be more accurate to say that Tunisia is the first to show the effects of a broader trend in the Arab world that is leading to democracy. They all have faux democracy with election results and parliaments and all the outward appearance of democracy (CORRECTION: well, Iraq has real--if fragile--democracy, so Iraq is clearly not vulnerable to a Tunisia contagion). Why wouldn't people in time expect more than the form of democracy? How long such a trend could take to affect more of the Arab world is unknowable.
But just dismissing the chances for copycat revolts is too easy, I think. I'd be more impressed with the uniqueness of Tunisia that proves only Tunisia can overturn tyrants if Kaplan could point to a pre-crisis article where he argues that the uniqueness of Tunisia makes them the prime candidate for a successful uprising.
Whether trend leader or domino, Tunisia deserves our support for achieving democracy there. And the wider Arab world that suffers under the misrule of autocrats deserves that support, too, if it one day can lead to more states following the path that Tunisia is on so far.