Not true. You cannot use HTTP error codes for everything. What if you were to use a service where you needed to retieve a record. In SOAP, you don't have to parse the response content manually. It'd be returned back to you as your toolkit provides for you, either as a hash, an object or /something/.
In REST, i have to put the effort in to take the format and use something on it, whether it's a comma delimited parsing module, an xml parsing module or something custom.
Look at the perlmonks XML services. If it were in SOAP, I wouldn't need to run an XML parser on them. All of my data would automagically, by the toolkit, be passed back as a hash or set of objects.. or set of arrays. Less to think about.