Today's SEO/SEM should have a thorough understanding of basic usability issues, html coding and validation, use of cascading style sheets and web copywriting skills.
Most clients are going to opt for a PFI (pay for inclusion) program also. That's where your skills and talent set will come into play in factoring the overall ROI of the clients online marketing campaign. You still need to optimize content for the web and we're not just talking search engines here. We're talking about usability, functionality, cross platform compatibility, and a host of other issues that need to be addressed in a well rounded search engine marketing campaign.
You need to become a diversified consultant and be able to offer the client added services which will provide balance in the campaign. Get your hat rack ready because you'll be wearing a bunch of different ones in your tenure as a professional search engine marketer!