In addition many of the skillsets are repetitive. Internet Marketing is a category, SEM incorporates paid and organic. If you want to list keywords to explain skillsets you can do so but I'd suggest that it's better to offer a solution (we optimize your business from search to conversion) than a tactic (we optimize your seo, ppc, bounce rate, landing pages, funnel, etc).
Social Media is an entire field as is Ecommerce conversion / funnel optimization. Two very different groups are looking for these offerings and while it's great to say you're a social media marketer who can think through the funnel, that's a far cry from being an "expert" in both.
It is possible to be broad but increasingly rare. Those of us who started in this field 10+ years ago accumulated skills as the web changed but while I may know dozens of topics, I don't proclaim to be an expert in all of them and, for the sake of focusing my business and providing a clear sense of offering to potential clients / employees, I've narrow in on a few areas I feel I am best at and are the most important for the market right now.
Focus is crucial.