My understanding of the 50AMP RV service is a little different. I think a RV electric service pedestal actually provides a RV with two 50AMP phases. This means that the RV would actually receive a total of 100AMP or about 12,000 watts.
You are right about the 50 Amp RV service, two 50 Amp 120V lines vs one 30 Amp 120V line. There is an amazing capacity difference between the two, 12,000 watts vs 3,600 watts.