Culturally there's a big difference, too. While in Europe unions and corporations tolerate and even co-operate with each other (German companies have, I believe, half of their board members controlled by labor unions), in the USA they are very antagonistic.
Either because of that or causing that, most unions in the USA are effectively nominal with no real power.
[1] http://en.wikipedia.org/wiki/Labor_unions_in_the_United_Stat...
[2] http://www.motherjones.com/politics/2012/03/what-are-right-t...
Perhaps within the last 100 years, but not "historically" in a general or broad sense. The historical ruling class didn't have professions, they had power.
Edit: If I may elaborate on this.
Also, i did not mean the political sense of "ruling class". I meant, strictly speaking, their status as economic agents. If you are a partner in a partnership, you have legal control rights. Same as if you are a material shareholder in a stock-company. You are not an "at-arms-lenght-employee" in other-words. So, the idea that you would need a union for what were in essence "company directors" just does not make logical sense. Again, that changes when (whatever the expertise) thes folks are forced to work for the state; they are then stripped of their control rights and take on a position more akin to Labour, structurally.