[WS:] Organizations are not created equal. Communist organizations that emphasize party discipline were more successful in organizing under adverse conditions (e.g. fascist dictatorship) than liberal organizations (which simply caved in to pressure). However liberal organizations 9such as social democratic parties) have been much more successful in parliamentary systems. In democracies, people have no stomach for communist style party discipline.
I think you are absolutely right that changes in the workplace made the "traditional" labor organizing very difficult, if not impossible. However, left wing parties were caught with their pants down during that change - for one reason or another they failed to appeal to the new working class, which is mostly either white collar and professional or "deskilled" service workers. White collar professional seem to be attracted to market neo-liberalism than traditional socialist or social democratic ideologies. Keep it in mind that it was, for a large part, left-leaning professionals who were instrumental in implementing major social reforms in the 20th century.
As to the service workers - it is not that they they cannot be organized, but they have to enough stakes in their current jobs to accept personal risk entailed by organizing. Most service jobs are crappy - so crappy that most people view them as temporary. People just do not want to invest their energies to organize on jobs that they know they will quit as soon as a slightly better opportunity arises.
And then there is the big trans-Atlantic divide. European left-of the center parties may appear lethargic or losing touch with their base, but they still have organization that wins them elections. So at least in principle, these parties have the capacity of being conduits of social change (I am talking reforms not a revolution here!). In the US otoh no such parties exist - the left of the center has zero political representation. Therefore, the US left faces a very different challenge than the Euro left - in addition to mobilizing its supporters it needs to win the right to suffrage that has been subverted by the electoral system and the two political parties.
Wojtek