In support of at least one of WWW's points I would say that having done a PPL in Canada (which admittedly is a whole lot different to a US license, but bear with me), coming back to the UK the R/T was by far and away the most difficult thing to convert.
The R/T in the UK is not only a lot more complex but it also uses a completely different terminology set (even clearences), which combined with learning new airspace is a major trial. I'd say four hours of conversion time is conservative if you're anywhere busy, and it'd probably help to own a scanner to help you attune yourself.
Am I correct in thinking that there is also no hood work requirement of any kind in an FAA PPL?