That is the fault of his overly deterministic "world system" approach.
>From a more historically contingent perspective, there is no "system"
only various outcomes of the local power struggles. Thus it is possible
to have a nominally capitalist system that works mainly for the whole
society rather than a select few, if the power of the owners are
effectively counterbalanced by that of the working class - like in
Norway or Sweden. Or you can have the US outcome, where the corporate
execs call all the shots and face little resistance. None of these two
outcomes was pre-ordained by the purported "logic" of capitalism, both
were products of historical contingencies.
Pushing that line of though even further, political participation (not limited to voting, of course) does make a big difference and the attitude " all politicians are the same, let's make a truly radical social change" is a bunch of steaming crap. But having said that, at this historical juncture, odds are very much against any effective participation and change, at least in the US. And it is not because Mr. Kerry or Mr. Dean lack proper leftist credentials, but because the corporate class wields enormous power that is not counterbalance by anything. I dare to say that under the current conditions even Karl Marx himself would not do much better than any of the "despised" Democrats, if elected president. Easing the yoke is the best we can hope for the moment.
Wojtek